Progressive Tax C#

Program.cs

var taxBands = new List<TaxBand>()
{
    new() {
    LowerLimit = 0,
    UpperLimit = 11600,
    RateInPercent = 10
},
        new() {
    LowerLimit = 11601,
    UpperLimit = 47150,
    RateInPercent = 12
},
            new() {
    LowerLimit = 47151,
    UpperLimit = 100525,
    RateInPercent = 22
},
new() {
    LowerLimit = 100526,
    UpperLimit = 191950,
    RateInPercent = 24
},
new() {
    LowerLimit = 191951,
    UpperLimit = 243725,
    RateInPercent = 32
},
new() {
    LowerLimit = 243726,
    UpperLimit = 609350,
    RateInPercent = 35
},
new() {
    LowerLimit = 609351,
    UpperLimit = decimal.MaxValue,
    RateInPercent = 37
}
};


decimal income = 50000;

var tax = CalculateProgressiveTaxWorkingImprovedD(income, taxBands);

Console.WriteLine($"Tax for {income} is - {tax} and Tax Percentage to Income is {GetTaxPercentRelativeToIncome(income, tax)}%");

Console.ReadKey();


static decimal GetTaxPercentRelativeToIncome(decimal income, decimal tax)
{
    return income > 0 ? (tax / income) * 100 : 0;
}


static decimal CalculateProgressiveTaxWorkingOriginal(decimal income, List<TaxBand> taxBands)
{
    decimal tax = 0;
    bool isCompleted = false;

    foreach (var band in taxBands)
    {
        decimal taxableBandAmount = 0;
        var bandTaxPercentAmount = (band.RateInPercent / 100);

        if (band.UpperLimit >= income)
        {
            taxableBandAmount = (income - band.LowerLimit);
            isCompleted = true;
        }
        else
        {
            taxableBandAmount = (band.UpperLimit - band.LowerLimit);
        }

        tax += (taxableBandAmount * bandTaxPercentAmount);

        if (isCompleted)
            break;
    }

    return tax;
}

static decimal CalculateProgressiveTaxWorkingImprovedA(decimal income, List<TaxBand> taxBands)
{
    decimal tax = 0;

    foreach (var band in taxBands)
    {
        if (income <= band.LowerLimit)
            continue;

        decimal taxableAmountInBand = Math.Min(income, band.UpperLimit) - band.LowerLimit;
        decimal taxInBand = taxableAmountInBand * (band.RateInPercent / 100);
        tax += taxInBand;
    }

    return tax;
}

static decimal CalculateProgressiveTaxWorkingMeImprovedB(decimal income, List<TaxBand> taxBands)
{
    decimal tax = 0;

    foreach (var band in taxBands)
    {
        if (income <= band.LowerLimit)
            break;

        decimal taxableAmountInBand = Math.Min(income - band.LowerLimit, band.UpperLimit - band.LowerLimit);
        tax += taxableAmountInBand * (band.RateInPercent / 100);
    }

    return tax;
}

static decimal CalculateProgressiveTaxWorkingMeImprovedC(decimal income, List<TaxBand> taxBands)
{
    decimal tax = 0;
    decimal previousUpperLimit = 0;

    foreach (var band in taxBands)
    {
        decimal lowerLimit = band.LowerLimit;
        decimal upperLimit = band.UpperLimit;
        decimal rateInPercent = band.RateInPercent;

        if (income <= lowerLimit)
            break;

        decimal taxableAmountInBand = Math.Min(income, upperLimit) - Math.Max(previousUpperLimit, lowerLimit);
        tax += taxableAmountInBand * (rateInPercent / 100);

        previousUpperLimit = upperLimit;
    }

    return tax;
}

static decimal CalculateProgressiveTaxWorkingImprovedD(decimal income, List<TaxBand> taxBands)
{
    decimal tax = 0;

    // Filter tax bands applicable to the given income
    var applicableTaxBands = taxBands.Where(band => income > band.LowerLimit).ToList();

    foreach (var band in applicableTaxBands)
    {
        //decimal taxableAmountInBand = Math.Min(income, band.UpperLimit) - band.LowerLimit;
        decimal taxableAmountInBand = Math.Min(income - band.LowerLimit, band.UpperLimit - band.LowerLimit);
        decimal taxInBand = taxableAmountInBand * (band.RateInPercent / 100);
        tax += taxInBand;
    }

    return tax;
}


public class TaxBand
{
    public decimal LowerLimit { get; set; }
    public decimal UpperLimit { get; set; }
    public decimal RateInPercent { get; set; }
}