CertiPay.Taxes.Federal includes several useful calculators and the Federal income tax tables for use in calculating payroll taxes.
It depends on some classes available in CertiPay.Payroll.Common also available on GitHub and NuGet.
Most of the calculators are straight-forward and have self-explanatory parameters.
IAnnualizedIncomeCalculator calc = new AnnualizedIncomeCalculator();
Decimal result = calc.Calculate(year: 2014, grossIncomeForPeriod: 1000, frequency: PayrollFrequency.Weekly, withholdingAllowances: 2);