How we calculate

Last reviewed: October 18, 2026

Every calculator on ToolsForNumbers uses standard, widely published formulas. Each calculator page shows its formula and a worked example. This page collects the key assumptions and sources in one place.

Taxes (2026)

• Federal income tax brackets and standard deductions for 2026: single $16,100, married filing jointly $32,200, head of household $24,150.
• Social Security: 6.2% of wages up to $184,500.
• Medicare: 1.45% of all wages, plus an additional 0.9% above $200,000 for single filers.
• State income tax is applied as a flat rate you enter, which is an approximation for states with progressive brackets.

Sources:

• IRS Rev. Proc. 2025-32 (2026 inflation adjustments: brackets and standard deduction)
• Social Security Administration: 2026 contribution and benefit base

Loans and mortgages

Payments use the standard fixed-rate amortization formula with monthly compounding. Mortgage estimates add property tax and insurance (divided by 12), HOA fees, and PMI as a yearly percentage of the loan when the down payment is under 20%. Real lender quotes also depend on your credit, fees and points.

Savings and retirement

Growth is simulated month by month. Investment returns are assumptions, not predictions; real returns vary from year to year and can be negative. Retirement income uses the 4% rule as a rough guide.

Dates

Date calculations use your device's calendar and time zone. Holiday dates follow US federal rules (for example, Thanksgiving is the fourth Thursday of November) and Western (Gregorian) Easter.

Not financial advice

Our calculators give estimates for general information. They aren't financial, tax, legal or medical advice. For decisions that matter, check with a qualified professional.

Found an error? Please let us know. Corrections are made quickly and this page is updated each tax year.