out

Taxes in asturias
Gross: 420000, Net: 220831 (18402 / mo), Tax: 199168 - 47.42 percent goes to taxes
Gross: 245200, Net: 135179 (11264 / mo), Tax: 110020 - 44.87 percent goes to taxes
Gross: 180000, Net: 103231 (8602 / mo), Tax: 76768 - 42.65 percent goes to taxes
Gross: 157700, Net: 92131 (7677 / mo), Tax: 65568 - 41.58 percent goes to taxes
Gross: 113950, Net: 70256 (5854 / mo), Tax: 43693 - 38.34 percent goes to taxes
Gross: 92075, Net: 59318 (4943 / mo), Tax: 32756 - 35.58 percent goes to taxes
Gross: 70200, Net: 47391 (3949 / mo), Tax: 22808 - 32.49 percent goes to taxes

Taxes in bizkaia
Gross: 420000, Net: 228562 (19046 / mo), Tax: 191438 - 45.58 percent goes to taxes
Gross: 245200, Net: 139414 (11617 / mo), Tax: 105786 - 43.14 percent goes to taxes
Gross: 180000, Net: 106162 (8846 / mo), Tax: 73838 - 41.02 percent goes to taxes
Gross: 157700, Net: 94353 (7862 / mo), Tax: 63346 - 40.17 percent goes to taxes
Gross: 113950, Net: 71075 (5922 / mo), Tax: 42874 - 37.63 percent goes to taxes
Gross: 92075, Net: 59260 (4938 / mo), Tax: 32814 - 35.64 percent goes to taxes
Gross: 70200, Net: 47229 (3935 / mo), Tax: 22971 - 32.72 percent goes to taxes

taxes.rb

taxes = {
  asturias: {
    12_450 => 20,
    17_707 => 24,
    33_007 => 28,
    53_407 => 37,
    70_000 => 43,
    90_000 => 45,
    175_000 => 50,
    1_000_000_000_000 => 51
  },
  bizkaia: {
    15_550 => 23,
    31_100 => 28,
    46_650 => 35,
    66_640 => 40,
    92_310 => 45,
    123_070 => 46,
    179_460 => 47,
    1_000_000_000_000 => 49
  }
}

def tax(amount, brackets)
  sum = 0
  previous = 0
  brackets.each do | bracket, percent |
    last = amount < bracket
    base = (last ? amount : bracket) - previous
    sum += base * percent / 100.0
    break if last
    previous = bracket
  end
  sum
end

taxes.each do | place, brackets |
  puts "Taxes in #{place}"
  %w(420000 245200 180000 157700 113950 92075 70200).map(&:to_f).map do | salary |
    tax = tax(salary, brackets)
    net = salary - tax
    net_12 = net / 12.0
    tax_100 = tax / salary * 100
    printf("Gross: %d, Net: %d (%d / mo), Tax: %d - %.2f percent goes to taxes\n", salary, net, net_12, tax, tax_100)
  end
  puts
end