About

Why this exists

Most financial decisions come down to arithmetic that is simple in principle and surprisingly easy to get wrong. A mortgage payment is not just principal and interest. A raise does not reduce your take-home pay. Removing sales tax is not subtraction. Each of those is a common mistake with a real cost.

These calculators exist to make that arithmetic visible. Every tool shows its formula, states its assumptions, and works through a concrete example so you can check the result against your own situation rather than taking a number on faith.

How the calculators are built

The calculation engine is a set of pure functions with no dependencies and no hidden state. Given the same inputs, every calculator produces the same output, and the logic can be read and verified independently of the interface.

Everything runs client-side in your browser. The numbers you type are never transmitted to a server, logged, or stored.

Accuracy and limitations

Tax figures use published federal tables for the tax year stated on the page. Rates, brackets and contribution limits change annually, and the tables are updated when new figures are released.

• Federal only. State and local income taxes vary too widely to model generically, and are left as an input where relevant.
• No credits or itemized deductions. The income tax calculator applies the standard deduction and the bracket schedule.
• Constant assumptions. Projections use a single fixed rate of return rather than a range, which real markets never deliver.
• Planning estimates, not quotes. Lender offers, insurance premiums and actual tax liability always come from the institution or agency itself.

Corrections

If you find an error, please report it. Corrections to a formula, an outdated tax figure or a misleading explanation are all worth fixing, and reports are read.

How the site is funded

The site is free to use and supported by advertising. Ad slots are clearly separated from content and are never placed inside a calculator's results. Advertising has no influence on what the calculators compute or what the guides say.