Methodology, Formulas & Legal Tax Tables (2026)

1. U.S. Federal Income Tax & FICA (2026)

Federal taxable income is computed by subtracting the 2026 standard deduction ($15,000 for single filers) from gross annual wages, then applying the 7 progressive IRS marginal brackets (10%, 12%, 22%, 24%, 32%, 35%, and 37%). FICA comprises 6.2% Social Security up to $176,100 plus 1.45% Medicare on all wages (and 0.9% Additional Medicare Tax above $200,000).

2. PITI Mortgage Amortization

Monthly Principal & Interest uses the standard fixed-rate annuity equation M = P · [r(1+r)^n] / [(1+r)^n − 1], combined with state-specific effective property tax rates, hazard insurance, and PMI when down payment is under 20%.