hinrik/dutch_mortgage.pl

## dutch_mortgage.pl
use 5.14.0;
use warnings;
use Getopt::Long qw(:config no_ignore_case bundling);
use List::Util 'sum';
use Spreadsheet::Engine::Function::PMT;

# up to date as of 2014
my $max_deduction    = 51.5;
my $min_deduction    = 42;
my $yearly_reduction = 5;
my $tax_credit       = 2103;
my $invest_return    = 5;
my @tax_brackets = (
    [19_645, 5.1],
    [13_718, 10.85],
    [23_168, 42],
    [999999, 52],
);

my %args;
my $success = GetOptions(
    'p|principal=s'   => \my $principal,
    's|salary=s'      => \my $salary,
    't|term=s@'       => \my @terms,
    'b|bump=s'        => \(my $bump = 0),
    'r|ruling=s'      => \(my $ruling_years = 0),
);

if (!$success || !$principal || !$salary || !@terms) {
    die "Usage: perl mort.pl --principal=250000 --salary=50000 --bump=3 --ruling=5 --term 10:3.5 --term 20:4.5\n";
}

@terms = map { [split /:/, $_] } @terms;
my $years = sum(map { $_->[0] } @terms);
my $annuity = calculate_annuity($principal, $years, \@terms);
my $linear = calculate_linear($principal, $years, \@terms);
add_aggregates_and_net($_, $salary, $bump, $tax_credit, $max_deduction, $yearly_reduction, $ruling_years) for $annuity, $linear;

print "\n";
printf "Mortgage duration:   %i years\n", $years;
printf "Principal amount:    %i\n", $principal;
printf "Gross yearly salary: %i\n", $salary;
printf "Yearly salary bump:  %i%%\n", $bump || 0;
printf "30%% ruling for:      %i years\n", $ruling_years;
print "\nInterest terms:\n";
printf "  %2i years @ %.2f%%\n", @$_ for @terms;
print "\n";

compare($years, $annuity, $linear);

for my $m (['Annuity', $annuity], ['Linear', $linear]) {
    my ($type, $mortgage) = @$m;

    print "$type\n------------------\n";
    printf("Gross cost: %6i\n", $mortgage->{gross});
    printf("Deduction:  %6i\n", $mortgage->{gross} - $mortgage->{net});
    printf("Net cost:   %6i\n", $mortgage->{net});

    for my $year_no (1..@{ $mortgage->{years} }) {
        my $year = $mortgage->{years}[$year_no-1];
        printf "\nYear %2i  (%.2f%%)", $year_no, $year->{rate};
        printf "  Repayment: %5i", $year->{repayment};
        printf "  Interest: %5i", $year->{interest};
        printf "  Gross: %5i", $year->{gross};
        printf "  Deduction: %5i", $year->{gross} - $year->{net};
        printf "  Net: %5i", $year->{net};
        printf "  Avg monthly gross: %4i", $year->{gross} / 12;
        printf "  Avg monthly net: %4i", $year->{net} / 12;
    }
    print "\n\n\n";
}

# fixed monthly gross (principal+interest) payments
sub calculate_annuity {
    my ($principal, $years, $terms) = @_;
    my %mortgage;

    for my $term (@$terms) {
        my ($term_years, $yearly_rate) = @$term;
        my $monthly_gross = -Spreadsheet::Engine::Function::PMT->calculate(
            (1+$yearly_rate/100)**(1/12)-1, $years * 12, $principal,
        );

        for (1..$term_years) {
            my %year = (rate => $yearly_rate);

            for my $month (1..12) {
                my $monthly_interest = ($principal * $yearly_rate/100) / 12;
                my $monthly_repayment = $monthly_gross - $monthly_interest;
                $principal -= $monthly_repayment;
                push @{ $year{months} }, {
                    gross     => $monthly_gross,
                    interest  => $monthly_interest,
                    repayment => $monthly_repayment,
                };
            }
            push @{ $mortgage{years} }, \%year;
        }

        $years -= $term_years;
    }

    return \%mortgage;
}

# fixed monthly principal payments
sub calculate_linear {
    my ($principal, $years, $terms) = @_;
    my %mortgage;

    my $monthly_repayment = $principal / $years / 12;
    for my $term (@$terms) {
        my ($term_years, $yearly_rate) = @$term;

        for (1..$term_years) {
            my %year = (rate => $yearly_rate);
            for (1..12) {
                my $monthly_interest = ($principal * $yearly_rate/100) / 12;
                my $monthly_gross = $monthly_repayment + $monthly_interest;
                $principal -= $monthly_repayment;
                push @{ $year{months} }, {
                    gross     => $monthly_gross,
                    interest  => $monthly_interest,
                    repayment => $monthly_repayment,
                };
            }
            push @{ $mortgage{years} }, \%year;
        }
    }

    return \%mortgage;
}

sub add_aggregates_and_net {
    my ($mortgage, $salary, $bump, $tax_credit, $max_deduction, $yearly_reduction, $ruling_years) = @_;

    for my $year (@{ $mortgage->{years} }) {
        my $taxable_salary    = $ruling_years ? $salary * 0.7 : $salary;
        $taxable_salary      -= $tax_credit;
        my $yearly_interest   = sum(map { $_->{interest} } @{ $year->{months} });
        my $yearly_refund     = tax($taxable_salary, $max_deduction) - tax($taxable_salary-$yearly_interest, $max_deduction);
        my $yearly_gross      = sum(map { $_->{gross} } @{ $year->{months} });

        for my $month (@{ $year->{months} }) {
            my $monthly_refund = $month->{interest} / $yearly_interest * $yearly_refund;
            $month->{net} = $month->{gross} - $monthly_refund;
        }

        $year->{gross}     = $yearly_gross;
        $year->{interest}  = $yearly_interest;
        $year->{net}       = $yearly_gross - $yearly_refund;
        $year->{repayment} = sum(map { $_->{repayment} } @{ $year->{months} });

        $salary *= (1+$bump/100) if $bump;
        $ruling_years-- if $ruling_years;
        $max_deduction -= $yearly_reduction if $max_deduction > $min_deduction;
    }

    for my $amount (qw(interest net gross)) {
        $mortgage->{$amount} = sum(map { $_->{$amount} } @{ $mortgage->{years} } );
    }
    return;
}

sub tax {
    my ($salary, $max_deduction) = @_;

    my $tax;
    for my $bracket (@tax_brackets) {
        my ($level, $rate) = @$bracket;
        my $taxable = $salary >= $level ? $level : $salary;
        $rate = $max_deduction if $max_deduction && $rate > $max_deduction;
        $tax += $taxable * ($rate/100);
        $salary -= $taxable;
        last if !$salary;
    }

    return $tax;
}

sub compare {
    my ($years, $annuity, $linear) = @_;

    say <<BLURB;
If we take the difference in net yearly mortgage payments and calculate
an ROI of 5%, we can see which type of mortgage is cheaper in the long
run if you are investing your spare income in index funds with a 5% return.
The annuity mortgage has a higher net payment total than a linear mortgage,
but the extra investment returns can more than make up for it due to the
annuity mortgage's higher ratio of (tax-deductible) interest to principal
payments, especially in the early years.
BLURB

    my $linear_invest = 0;
    my $annuity_invest = 0;
    for my $year (0..$years-1) {
        my $linear_net = $linear->{years}[$year]{net};
        my $annuity_net = $annuity->{years}[$year]{net};

        if ($linear_net > $annuity_net) {
            $annuity_invest += $linear_net - $annuity_net;
        }
        elsif ($annuity_net > $linear_net) {
            $linear_invest += $annuity_net - $linear_net;
        }
        $annuity_invest *= (1+$invest_return/100);
        $linear_invest *= (1+$invest_return/100);
    }
    printf "  Annuity investment earnings: %6i\n", $annuity_invest;
    printf "  Linear investment earnings:  %6i\n", $linear_invest;
    print "\n";
}

## example_output.txt
$ perl dutch_mortgage.pl -p 250000 -s 50000 -r 5 -b 3 -t 10:3.25 -t 10:5 -t 10:6.5

Mortgage duration:   30 years
Principal amount:    250000
Gross yearly salary: 50000
Yearly salary bump:  3%
30% ruling for:      5 years

Interest terms:
  10 years @ 3.25%
  10 years @ 5.00%
  10 years @ 6.50%

If we take the difference in net yearly mortgage payments and calculate
an ROI of 5%, we can see which type of mortgage is cheaper in the long
run if you are investing your spare income in index funds with a 5% return.
The annuity mortgage has a higher net payment total than a linear mortgage,
but the extra investment returns can more than make up for it due to the
annuity mortgage's higher ratio of (tax-deductible) interest to principal
payments, especially in the early years.

  Annuity investment earnings:  98331
  Linear investment earnings:   65233

Annuity
------------------
Gross cost: 445536
Deduction:   72873
Net cost:   372662

Year  1  (3.25%)  Repayment:  4926  Interest:  8052  Gross: 12978  Deduction:   873  Net: 12104  Avg monthly gross: 1081  Avg monthly net: 1008
Year  2  (3.25%)  Repayment:  5088  Interest:  7889  Gross: 12978  Deduction:  1037  Net: 11940  Avg monthly gross: 1081  Avg monthly net:  995
Year  3  (3.25%)  Repayment:  5256  Interest:  7721  Gross: 12978  Deduction:  1348  Net: 11629  Avg monthly gross: 1081  Avg monthly net:  969
Year  4  (3.25%)  Repayment:  5429  Interest:  7548  Gross: 12978  Deduction:  1670  Net: 11307  Avg monthly gross: 1081  Avg monthly net:  942
Year  5  (3.25%)  Repayment:  5609  Interest:  7369  Gross: 12978  Deduction:  2003  Net: 10975  Avg monthly gross: 1081  Avg monthly net:  914
Year  6  (3.25%)  Repayment:  5794  Interest:  7184  Gross: 12978  Deduction:  2981  Net:  9996  Avg monthly gross: 1081  Avg monthly net:  833
Year  7  (3.25%)  Repayment:  5985  Interest:  6992  Gross: 12978  Deduction:  2902  Net: 10076  Avg monthly gross: 1081  Avg monthly net:  839
Year  8  (3.25%)  Repayment:  6182  Interest:  6795  Gross: 12978  Deduction:  2820  Net: 10158  Avg monthly gross: 1081  Avg monthly net:  846
Year  9  (3.25%)  Repayment:  6386  Interest:  6591  Gross: 12978  Deduction:  2735  Net: 10242  Avg monthly gross: 1081  Avg monthly net:  853
Year 10  (3.25%)  Repayment:  6597  Interest:  6380  Gross: 12978  Deduction:  2648  Net: 10330  Avg monthly gross: 1081  Avg monthly net:  860
Year 11  (5.00%)  Repayment:  5613  Interest:  9509  Gross: 15122  Deduction:  3946  Net: 11176  Avg monthly gross: 1260  Avg monthly net:  931
Year 12  (5.00%)  Repayment:  5900  Interest:  9222  Gross: 15122  Deduction:  3827  Net: 11295  Avg monthly gross: 1260  Avg monthly net:  941
Year 13  (5.00%)  Repayment:  6202  Interest:  8920  Gross: 15122  Deduction:  3702  Net: 11420  Avg monthly gross: 1260  Avg monthly net:  951
Year 14  (5.00%)  Repayment:  6519  Interest:  8603  Gross: 15122  Deduction:  3570  Net: 11552  Avg monthly gross: 1260  Avg monthly net:  962
Year 15  (5.00%)  Repayment:  6852  Interest:  8269  Gross: 15122  Deduction:  3431  Net: 11690  Avg monthly gross: 1260  Avg monthly net:  974
Year 16  (5.00%)  Repayment:  7203  Interest:  7919  Gross: 15122  Deduction:  3286  Net: 11836  Avg monthly gross: 1260  Avg monthly net:  986
Year 17  (5.00%)  Repayment:  7572  Interest:  7550  Gross: 15122  Deduction:  3133  Net: 11989  Avg monthly gross: 1260  Avg monthly net:  999
Year 18  (5.00%)  Repayment:  7959  Interest:  7163  Gross: 15122  Deduction:  2972  Net: 12149  Avg monthly gross: 1260  Avg monthly net: 1012
Year 19  (5.00%)  Repayment:  8366  Interest:  6756  Gross: 15122  Deduction:  2803  Net: 12318  Avg monthly gross: 1260  Avg monthly net: 1026
Year 20  (5.00%)  Repayment:  8794  Interest:  6327  Gross: 15122  Deduction:  2626  Net: 12496  Avg monthly gross: 1260  Avg monthly net: 1041
Year 21  (6.50%)  Repayment:  8797  Interest:  7655  Gross: 16452  Deduction:  3176  Net: 13275  Avg monthly gross: 1371  Avg monthly net: 1106
Year 22  (6.50%)  Repayment:  9386  Interest:  7066  Gross: 16452  Deduction:  2932  Net: 13520  Avg monthly gross: 1371  Avg monthly net: 1126
Year 23  (6.50%)  Repayment: 10015  Interest:  6437  Gross: 16452  Deduction:  2671  Net: 13781  Avg monthly gross: 1371  Avg monthly net: 1148
Year 24  (6.50%)  Repayment: 10685  Interest:  5766  Gross: 16452  Deduction:  2393  Net: 14059  Avg monthly gross: 1371  Avg monthly net: 1171
Year 25  (6.50%)  Repayment: 11401  Interest:  5051  Gross: 16452  Deduction:  2096  Net: 14356  Avg monthly gross: 1371  Avg monthly net: 1196
Year 26  (6.50%)  Repayment: 12165  Interest:  4287  Gross: 16452  Deduction:  1779  Net: 14673  Avg monthly gross: 1371  Avg monthly net: 1222
Year 27  (6.50%)  Repayment: 12979  Interest:  3472  Gross: 16452  Deduction:  1441  Net: 15011  Avg monthly gross: 1371  Avg monthly net: 1250
Year 28  (6.50%)  Repayment: 13849  Interest:  2603  Gross: 16452  Deduction:  1080  Net: 15372  Avg monthly gross: 1371  Avg monthly net: 1281
Year 29  (6.50%)  Repayment: 14776  Interest:  1676  Gross: 16452  Deduction:   695  Net: 15757  Avg monthly gross: 1371  Avg monthly net: 1313
Year 30  (6.50%)  Repayment: 15766  Interest:   686  Gross: 16452  Deduction:   284  Net: 16167  Avg monthly gross: 1371  Avg monthly net: 1347


Linear
------------------
Gross cost: 407803
Deduction:   56805
Net cost:   350998

Year  1  (3.25%)  Repayment:  8333  Interest:  8000  Gross: 16334  Deduction:   868  Net: 15466  Avg monthly gross: 1361  Avg monthly net: 1288
Year  2  (3.25%)  Repayment:  8333  Interest:  7730  Gross: 16063  Deduction:  1020  Net: 15042  Avg monthly gross: 1338  Avg monthly net: 1253
Year  3  (3.25%)  Repayment:  8333  Interest:  7459  Gross: 15792  Deduction:  1319  Net: 14472  Avg monthly gross: 1316  Avg monthly net: 1206
Year  4  (3.25%)  Repayment:  8333  Interest:  7188  Gross: 15521  Deduction:  1631  Net: 13889  Avg monthly gross: 1293  Avg monthly net: 1157
Year  5  (3.25%)  Repayment:  8333  Interest:  6917  Gross: 15250  Deduction:  1954  Net: 13296  Avg monthly gross: 1270  Avg monthly net: 1108
Year  6  (3.25%)  Repayment:  8333  Interest:  6646  Gross: 14980  Deduction:  2758  Net: 12221  Avg monthly gross: 1248  Avg monthly net: 1018
Year  7  (3.25%)  Repayment:  8333  Interest:  6375  Gross: 14709  Deduction:  2645  Net: 12063  Avg monthly gross: 1225  Avg monthly net: 1005
Year  8  (3.25%)  Repayment:  8333  Interest:  6105  Gross: 14438  Deduction:  2533  Net: 11904  Avg monthly gross: 1203  Avg monthly net:  992
Year  9  (3.25%)  Repayment:  8333  Interest:  5834  Gross: 14167  Deduction:  2421  Net: 11746  Avg monthly gross: 1180  Avg monthly net:  978
Year 10  (3.25%)  Repayment:  8333  Interest:  5563  Gross: 13896  Deduction:  2308  Net: 11587  Avg monthly gross: 1158  Avg monthly net:  965
Year 11  (5.00%)  Repayment:  8333  Interest:  8142  Gross: 16475  Deduction:  3379  Net: 13096  Avg monthly gross: 1372  Avg monthly net: 1091
Year 12  (5.00%)  Repayment:  8333  Interest:  7725  Gross: 16059  Deduction:  3206  Net: 12852  Avg monthly gross: 1338  Avg monthly net: 1071
Year 13  (5.00%)  Repayment:  8333  Interest:  7309  Gross: 15642  Deduction:  3033  Net: 12609  Avg monthly gross: 1303  Avg monthly net: 1050
Year 14  (5.00%)  Repayment:  8333  Interest:  6892  Gross: 15225  Deduction:  2860  Net: 12365  Avg monthly gross: 1268  Avg monthly net: 1030
Year 15  (5.00%)  Repayment:  8333  Interest:  6475  Gross: 14809  Deduction:  2687  Net: 12121  Avg monthly gross: 1234  Avg monthly net: 1010
Year 16  (5.00%)  Repayment:  8333  Interest:  6059  Gross: 14392  Deduction:  2514  Net: 11877  Avg monthly gross: 1199  Avg monthly net:  989
Year 17  (5.00%)  Repayment:  8333  Interest:  5642  Gross: 13975  Deduction:  2341  Net: 11634  Avg monthly gross: 1164  Avg monthly net:  969
Year 18  (5.00%)  Repayment:  8333  Interest:  5225  Gross: 13559  Deduction:  2168  Net: 11390  Avg monthly gross: 1129  Avg monthly net:  949
Year 19  (5.00%)  Repayment:  8333  Interest:  4809  Gross: 13142  Deduction:  1995  Net: 11146  Avg monthly gross: 1095  Avg monthly net:  928
Year 20  (5.00%)  Repayment:  8333  Interest:  4392  Gross: 12725  Deduction:  1822  Net: 10902  Avg monthly gross: 1060  Avg monthly net:  908
Year 21  (6.50%)  Repayment:  8333  Interest:  5168  Gross: 13501  Deduction:  2144  Net: 11356  Avg monthly gross: 1125  Avg monthly net:  946
Year 22  (6.50%)  Repayment:  8333  Interest:  4626  Gross: 12960  Deduction:  1920  Net: 11039  Avg monthly gross: 1080  Avg monthly net:  919
Year 23  (6.50%)  Repayment:  8333  Interest:  4085  Gross: 12418  Deduction:  1695  Net: 10723  Avg monthly gross: 1034  Avg monthly net:  893
Year 24  (6.50%)  Repayment:  8333  Interest:  3543  Gross: 11876  Deduction:  1470  Net: 10406  Avg monthly gross:  989  Avg monthly net:  867
Year 25  (6.50%)  Repayment:  8333  Interest:  3001  Gross: 11335  Deduction:  1245  Net: 10089  Avg monthly gross:  944  Avg monthly net:  840
Year 26  (6.50%)  Repayment:  8333  Interest:  2460  Gross: 10793  Deduction:  1020  Net:  9772  Avg monthly gross:  899  Avg monthly net:  814
Year 27  (6.50%)  Repayment:  8333  Interest:  1918  Gross: 10251  Deduction:   796  Net:  9455  Avg monthly gross:  854  Avg monthly net:  787
Year 28  (6.50%)  Repayment:  8333  Interest:  1376  Gross:  9710  Deduction:   571  Net:  9138  Avg monthly gross:  809  Avg monthly net:  761
Year 29  (6.50%)  Repayment:  8333  Interest:   835  Gross:  9168  Deduction:   346  Net:  8821  Avg monthly gross:  764  Avg monthly net:  735
Year 30  (6.50%)  Repayment:  8333  Interest:   293  Gross:  8626  Deduction:   121  Net:  8504  Avg monthly gross:  718  Avg monthly net:  708
	use 5.14.0;
	use warnings;
	use Getopt::Long qw(:config no_ignore_case bundling);
	use List::Util 'sum';
	use Spreadsheet::Engine::Function::PMT;

	# up to date as of 2014
	my $max_deduction = 51.5;
	my $min_deduction = 42;
	my $yearly_reduction = 5;
	my $tax_credit = 2103;
	my $invest_return = 5;
	my @tax_brackets = (
	[19_645, 5.1],
	[13_718, 10.85],
	[23_168, 42],
	[999999, 52],
	);

	my %args;
	my $success = GetOptions(
	'p\|principal=s' => \my $principal,
	's\|salary=s' => \my $salary,
	't\|term=s@' => \my @terms,
	'b\|bump=s' => \(my $bump = 0),
	'r\|ruling=s' => \(my $ruling_years = 0),
	);

	if (!$success \|\| !$principal \|\| !$salary \|\| !@terms) {
	die "Usage: perl mort.pl --principal=250000 --salary=50000 --bump=3 --ruling=5 --term 10:3.5 --term 20:4.5\n";
	}

	@terms = map { [split /:/, $_] } @terms;
	my $years = sum(map { $_->[0] } @terms);
	my $annuity = calculate_annuity($principal, $years, \@terms);
	my $linear = calculate_linear($principal, $years, \@terms);
	add_aggregates_and_net($_, $salary, $bump, $tax_credit, $max_deduction, $yearly_reduction, $ruling_years) for $annuity, $linear;

	print "\n";
	printf "Mortgage duration: %i years\n", $years;
	printf "Principal amount: %i\n", $principal;
	printf "Gross yearly salary: %i\n", $salary;
	printf "Yearly salary bump: %i%%\n", $bump \|\| 0;
	printf "30%% ruling for: %i years\n", $ruling_years;
	print "\nInterest terms:\n";
	printf " %2i years @ %.2f%%\n", @$_ for @terms;
	print "\n";

	compare($years, $annuity, $linear);

	for my $m (['Annuity', $annuity], ['Linear', $linear]) {
	my ($type, $mortgage) = @$m;

	print "$type\n------------------\n";
	printf("Gross cost: %6i\n", $mortgage->{gross});
	printf("Deduction: %6i\n", $mortgage->{gross} - $mortgage->{net});
	printf("Net cost: %6i\n", $mortgage->{net});

	for my $year_no (1..@{ $mortgage->{years} }) {
	my $year = $mortgage->{years}[$year_no-1];
	printf "\nYear %2i (%.2f%%)", $year_no, $year->{rate};
	printf " Repayment: %5i", $year->{repayment};
	printf " Interest: %5i", $year->{interest};
	printf " Gross: %5i", $year->{gross};
	printf " Deduction: %5i", $year->{gross} - $year->{net};
	printf " Net: %5i", $year->{net};
	printf " Avg monthly gross: %4i", $year->{gross} / 12;
	printf " Avg monthly net: %4i", $year->{net} / 12;
	}
	print "\n\n\n";
	}

	# fixed monthly gross (principal+interest) payments
	sub calculate_annuity {
	my ($principal, $years, $terms) = @_;
	my %mortgage;

	for my $term (@$terms) {
	my ($term_years, $yearly_rate) = @$term;
	my $monthly_gross = -Spreadsheet::Engine::Function::PMT->calculate(
	(1+$yearly_rate/100)*(1/12)-1, $years 12, $principal,
	);

	for (1..$term_years) {
	my %year = (rate => $yearly_rate);

	for my $month (1..12) {
	my $monthly_interest = ($principal * $yearly_rate/100) / 12;
	my $monthly_repayment = $monthly_gross - $monthly_interest;
	$principal -= $monthly_repayment;
	push @{ $year{months} }, {
	gross => $monthly_gross,
	interest => $monthly_interest,
	repayment => $monthly_repayment,
	};
	}
	push @{ $mortgage{years} }, \%year;
	}

	$years -= $term_years;
	}

	return \%mortgage;
	}

	# fixed monthly principal payments
	sub calculate_linear {
	my ($principal, $years, $terms) = @_;
	my %mortgage;

	my $monthly_repayment = $principal / $years / 12;
	for my $term (@$terms) {
	my ($term_years, $yearly_rate) = @$term;

	for (1..$term_years) {
	my %year = (rate => $yearly_rate);
	for (1..12) {
	my $monthly_interest = ($principal * $yearly_rate/100) / 12;
	my $monthly_gross = $monthly_repayment + $monthly_interest;
	$principal -= $monthly_repayment;
	push @{ $year{months} }, {
	gross => $monthly_gross,
	interest => $monthly_interest,
	repayment => $monthly_repayment,
	};
	}
	push @{ $mortgage{years} }, \%year;
	}
	}

	return \%mortgage;
	}

	sub add_aggregates_and_net {
	my ($mortgage, $salary, $bump, $tax_credit, $max_deduction, $yearly_reduction, $ruling_years) = @_;

	for my $year (@{ $mortgage->{years} }) {
	my $taxable_salary = $ruling_years ? $salary * 0.7 : $salary;
	$taxable_salary -= $tax_credit;
	my $yearly_interest = sum(map { $_->{interest} } @{ $year->{months} });
	my $yearly_refund = tax($taxable_salary, $max_deduction) - tax($taxable_salary-$yearly_interest, $max_deduction);
	my $yearly_gross = sum(map { $_->{gross} } @{ $year->{months} });

	for my $month (@{ $year->{months} }) {
	my $monthly_refund = $month->{interest} / $yearly_interest * $yearly_refund;
	$month->{net} = $month->{gross} - $monthly_refund;
	}

	$year->{gross} = $yearly_gross;
	$year->{interest} = $yearly_interest;
	$year->{net} = $yearly_gross - $yearly_refund;
	$year->{repayment} = sum(map { $_->{repayment} } @{ $year->{months} });

	$salary *= (1+$bump/100) if $bump;
	$ruling_years-- if $ruling_years;
	$max_deduction -= $yearly_reduction if $max_deduction > $min_deduction;
	}

	for my $amount (qw(interest net gross)) {
	$mortgage->{$amount} = sum(map { $_->{$amount} } @{ $mortgage->{years} } );
	}
	return;
	}

	sub tax {
	my ($salary, $max_deduction) = @_;

	my $tax;
	for my $bracket (@tax_brackets) {
	my ($level, $rate) = @$bracket;
	my $taxable = $salary >= $level ? $level : $salary;
	$rate = $max_deduction if $max_deduction && $rate > $max_deduction;
	$tax += $taxable * ($rate/100);
	$salary -= $taxable;
	last if !$salary;
	}

	return $tax;
	}

	sub compare {
	my ($years, $annuity, $linear) = @_;

	say <<BLURB;
	If we take the difference in net yearly mortgage payments and calculate
	an ROI of 5%, we can see which type of mortgage is cheaper in the long
	run if you are investing your spare income in index funds with a 5% return.
	The annuity mortgage has a higher net payment total than a linear mortgage,
	but the extra investment returns can more than make up for it due to the
	annuity mortgage's higher ratio of (tax-deductible) interest to principal
	payments, especially in the early years.
	BLURB

	my $linear_invest = 0;
	my $annuity_invest = 0;
	for my $year (0..$years-1) {
	my $linear_net = $linear->{years}[$year]{net};
	my $annuity_net = $annuity->{years}[$year]{net};

	if ($linear_net > $annuity_net) {
	$annuity_invest += $linear_net - $annuity_net;
	}
	elsif ($annuity_net > $linear_net) {
	$linear_invest += $annuity_net - $linear_net;
	}
	$annuity_invest *= (1+$invest_return/100);
	$linear_invest *= (1+$invest_return/100);
	}
	printf " Annuity investment earnings: %6i\n", $annuity_invest;
	printf " Linear investment earnings: %6i\n", $linear_invest;
	print "\n";
	}
	$ perl dutch_mortgage.pl -p 250000 -s 50000 -r 5 -b 3 -t 10:3.25 -t 10:5 -t 10:6.5

	Mortgage duration: 30 years
	Principal amount: 250000
	Gross yearly salary: 50000
	Yearly salary bump: 3%
	30% ruling for: 5 years

	Interest terms:
	10 years @ 3.25%
	10 years @ 5.00%
	10 years @ 6.50%

	If we take the difference in net yearly mortgage payments and calculate
	an ROI of 5%, we can see which type of mortgage is cheaper in the long
	run if you are investing your spare income in index funds with a 5% return.
	The annuity mortgage has a higher net payment total than a linear mortgage,
	but the extra investment returns can more than make up for it due to the
	annuity mortgage's higher ratio of (tax-deductible) interest to principal
	payments, especially in the early years.

	Annuity investment earnings: 98331
	Linear investment earnings: 65233

	Annuity
	------------------
	Gross cost: 445536
	Deduction: 72873
	Net cost: 372662

	Year 1 (3.25%) Repayment: 4926 Interest: 8052 Gross: 12978 Deduction: 873 Net: 12104 Avg monthly gross: 1081 Avg monthly net: 1008
	Year 2 (3.25%) Repayment: 5088 Interest: 7889 Gross: 12978 Deduction: 1037 Net: 11940 Avg monthly gross: 1081 Avg monthly net: 995
	Year 3 (3.25%) Repayment: 5256 Interest: 7721 Gross: 12978 Deduction: 1348 Net: 11629 Avg monthly gross: 1081 Avg monthly net: 969
	Year 4 (3.25%) Repayment: 5429 Interest: 7548 Gross: 12978 Deduction: 1670 Net: 11307 Avg monthly gross: 1081 Avg monthly net: 942
	Year 5 (3.25%) Repayment: 5609 Interest: 7369 Gross: 12978 Deduction: 2003 Net: 10975 Avg monthly gross: 1081 Avg monthly net: 914
	Year 6 (3.25%) Repayment: 5794 Interest: 7184 Gross: 12978 Deduction: 2981 Net: 9996 Avg monthly gross: 1081 Avg monthly net: 833
	Year 7 (3.25%) Repayment: 5985 Interest: 6992 Gross: 12978 Deduction: 2902 Net: 10076 Avg monthly gross: 1081 Avg monthly net: 839
	Year 8 (3.25%) Repayment: 6182 Interest: 6795 Gross: 12978 Deduction: 2820 Net: 10158 Avg monthly gross: 1081 Avg monthly net: 846
	Year 9 (3.25%) Repayment: 6386 Interest: 6591 Gross: 12978 Deduction: 2735 Net: 10242 Avg monthly gross: 1081 Avg monthly net: 853
	Year 10 (3.25%) Repayment: 6597 Interest: 6380 Gross: 12978 Deduction: 2648 Net: 10330 Avg monthly gross: 1081 Avg monthly net: 860
	Year 11 (5.00%) Repayment: 5613 Interest: 9509 Gross: 15122 Deduction: 3946 Net: 11176 Avg monthly gross: 1260 Avg monthly net: 931
	Year 12 (5.00%) Repayment: 5900 Interest: 9222 Gross: 15122 Deduction: 3827 Net: 11295 Avg monthly gross: 1260 Avg monthly net: 941
	Year 13 (5.00%) Repayment: 6202 Interest: 8920 Gross: 15122 Deduction: 3702 Net: 11420 Avg monthly gross: 1260 Avg monthly net: 951
	Year 14 (5.00%) Repayment: 6519 Interest: 8603 Gross: 15122 Deduction: 3570 Net: 11552 Avg monthly gross: 1260 Avg monthly net: 962
	Year 15 (5.00%) Repayment: 6852 Interest: 8269 Gross: 15122 Deduction: 3431 Net: 11690 Avg monthly gross: 1260 Avg monthly net: 974
	Year 16 (5.00%) Repayment: 7203 Interest: 7919 Gross: 15122 Deduction: 3286 Net: 11836 Avg monthly gross: 1260 Avg monthly net: 986
	Year 17 (5.00%) Repayment: 7572 Interest: 7550 Gross: 15122 Deduction: 3133 Net: 11989 Avg monthly gross: 1260 Avg monthly net: 999
	Year 18 (5.00%) Repayment: 7959 Interest: 7163 Gross: 15122 Deduction: 2972 Net: 12149 Avg monthly gross: 1260 Avg monthly net: 1012
	Year 19 (5.00%) Repayment: 8366 Interest: 6756 Gross: 15122 Deduction: 2803 Net: 12318 Avg monthly gross: 1260 Avg monthly net: 1026
	Year 20 (5.00%) Repayment: 8794 Interest: 6327 Gross: 15122 Deduction: 2626 Net: 12496 Avg monthly gross: 1260 Avg monthly net: 1041
	Year 21 (6.50%) Repayment: 8797 Interest: 7655 Gross: 16452 Deduction: 3176 Net: 13275 Avg monthly gross: 1371 Avg monthly net: 1106
	Year 22 (6.50%) Repayment: 9386 Interest: 7066 Gross: 16452 Deduction: 2932 Net: 13520 Avg monthly gross: 1371 Avg monthly net: 1126
	Year 23 (6.50%) Repayment: 10015 Interest: 6437 Gross: 16452 Deduction: 2671 Net: 13781 Avg monthly gross: 1371 Avg monthly net: 1148
	Year 24 (6.50%) Repayment: 10685 Interest: 5766 Gross: 16452 Deduction: 2393 Net: 14059 Avg monthly gross: 1371 Avg monthly net: 1171
	Year 25 (6.50%) Repayment: 11401 Interest: 5051 Gross: 16452 Deduction: 2096 Net: 14356 Avg monthly gross: 1371 Avg monthly net: 1196
	Year 26 (6.50%) Repayment: 12165 Interest: 4287 Gross: 16452 Deduction: 1779 Net: 14673 Avg monthly gross: 1371 Avg monthly net: 1222
	Year 27 (6.50%) Repayment: 12979 Interest: 3472 Gross: 16452 Deduction: 1441 Net: 15011 Avg monthly gross: 1371 Avg monthly net: 1250
	Year 28 (6.50%) Repayment: 13849 Interest: 2603 Gross: 16452 Deduction: 1080 Net: 15372 Avg monthly gross: 1371 Avg monthly net: 1281
	Year 29 (6.50%) Repayment: 14776 Interest: 1676 Gross: 16452 Deduction: 695 Net: 15757 Avg monthly gross: 1371 Avg monthly net: 1313
	Year 30 (6.50%) Repayment: 15766 Interest: 686 Gross: 16452 Deduction: 284 Net: 16167 Avg monthly gross: 1371 Avg monthly net: 1347


	Linear
	------------------
	Gross cost: 407803
	Deduction: 56805
	Net cost: 350998

	Year 1 (3.25%) Repayment: 8333 Interest: 8000 Gross: 16334 Deduction: 868 Net: 15466 Avg monthly gross: 1361 Avg monthly net: 1288
	Year 2 (3.25%) Repayment: 8333 Interest: 7730 Gross: 16063 Deduction: 1020 Net: 15042 Avg monthly gross: 1338 Avg monthly net: 1253
	Year 3 (3.25%) Repayment: 8333 Interest: 7459 Gross: 15792 Deduction: 1319 Net: 14472 Avg monthly gross: 1316 Avg monthly net: 1206
	Year 4 (3.25%) Repayment: 8333 Interest: 7188 Gross: 15521 Deduction: 1631 Net: 13889 Avg monthly gross: 1293 Avg monthly net: 1157
	Year 5 (3.25%) Repayment: 8333 Interest: 6917 Gross: 15250 Deduction: 1954 Net: 13296 Avg monthly gross: 1270 Avg monthly net: 1108
	Year 6 (3.25%) Repayment: 8333 Interest: 6646 Gross: 14980 Deduction: 2758 Net: 12221 Avg monthly gross: 1248 Avg monthly net: 1018
	Year 7 (3.25%) Repayment: 8333 Interest: 6375 Gross: 14709 Deduction: 2645 Net: 12063 Avg monthly gross: 1225 Avg monthly net: 1005
	Year 8 (3.25%) Repayment: 8333 Interest: 6105 Gross: 14438 Deduction: 2533 Net: 11904 Avg monthly gross: 1203 Avg monthly net: 992
	Year 9 (3.25%) Repayment: 8333 Interest: 5834 Gross: 14167 Deduction: 2421 Net: 11746 Avg monthly gross: 1180 Avg monthly net: 978
	Year 10 (3.25%) Repayment: 8333 Interest: 5563 Gross: 13896 Deduction: 2308 Net: 11587 Avg monthly gross: 1158 Avg monthly net: 965
	Year 11 (5.00%) Repayment: 8333 Interest: 8142 Gross: 16475 Deduction: 3379 Net: 13096 Avg monthly gross: 1372 Avg monthly net: 1091
	Year 12 (5.00%) Repayment: 8333 Interest: 7725 Gross: 16059 Deduction: 3206 Net: 12852 Avg monthly gross: 1338 Avg monthly net: 1071
	Year 13 (5.00%) Repayment: 8333 Interest: 7309 Gross: 15642 Deduction: 3033 Net: 12609 Avg monthly gross: 1303 Avg monthly net: 1050
	Year 14 (5.00%) Repayment: 8333 Interest: 6892 Gross: 15225 Deduction: 2860 Net: 12365 Avg monthly gross: 1268 Avg monthly net: 1030
	Year 15 (5.00%) Repayment: 8333 Interest: 6475 Gross: 14809 Deduction: 2687 Net: 12121 Avg monthly gross: 1234 Avg monthly net: 1010
	Year 16 (5.00%) Repayment: 8333 Interest: 6059 Gross: 14392 Deduction: 2514 Net: 11877 Avg monthly gross: 1199 Avg monthly net: 989
	Year 17 (5.00%) Repayment: 8333 Interest: 5642 Gross: 13975 Deduction: 2341 Net: 11634 Avg monthly gross: 1164 Avg monthly net: 969
	Year 18 (5.00%) Repayment: 8333 Interest: 5225 Gross: 13559 Deduction: 2168 Net: 11390 Avg monthly gross: 1129 Avg monthly net: 949
	Year 19 (5.00%) Repayment: 8333 Interest: 4809 Gross: 13142 Deduction: 1995 Net: 11146 Avg monthly gross: 1095 Avg monthly net: 928
	Year 20 (5.00%) Repayment: 8333 Interest: 4392 Gross: 12725 Deduction: 1822 Net: 10902 Avg monthly gross: 1060 Avg monthly net: 908
	Year 21 (6.50%) Repayment: 8333 Interest: 5168 Gross: 13501 Deduction: 2144 Net: 11356 Avg monthly gross: 1125 Avg monthly net: 946
	Year 22 (6.50%) Repayment: 8333 Interest: 4626 Gross: 12960 Deduction: 1920 Net: 11039 Avg monthly gross: 1080 Avg monthly net: 919
	Year 23 (6.50%) Repayment: 8333 Interest: 4085 Gross: 12418 Deduction: 1695 Net: 10723 Avg monthly gross: 1034 Avg monthly net: 893
	Year 24 (6.50%) Repayment: 8333 Interest: 3543 Gross: 11876 Deduction: 1470 Net: 10406 Avg monthly gross: 989 Avg monthly net: 867
	Year 25 (6.50%) Repayment: 8333 Interest: 3001 Gross: 11335 Deduction: 1245 Net: 10089 Avg monthly gross: 944 Avg monthly net: 840
	Year 26 (6.50%) Repayment: 8333 Interest: 2460 Gross: 10793 Deduction: 1020 Net: 9772 Avg monthly gross: 899 Avg monthly net: 814
	Year 27 (6.50%) Repayment: 8333 Interest: 1918 Gross: 10251 Deduction: 796 Net: 9455 Avg monthly gross: 854 Avg monthly net: 787
	Year 28 (6.50%) Repayment: 8333 Interest: 1376 Gross: 9710 Deduction: 571 Net: 9138 Avg monthly gross: 809 Avg monthly net: 761
	Year 29 (6.50%) Repayment: 8333 Interest: 835 Gross: 9168 Deduction: 346 Net: 8821 Avg monthly gross: 764 Avg monthly net: 735
	Year 30 (6.50%) Repayment: 8333 Interest: 293 Gross: 8626 Deduction: 121 Net: 8504 Avg monthly gross: 718 Avg monthly net: 708