CalcFinch is a collection of 90 free online calculators for personal finance, health and fitness, math, conversions and dates. Our goal is simple: give you a correct answer quickly, and show you how it was calculated so you can trust it.
How we build our calculators
- Established formulas. We use standard, published methods — the amortization formula lenders use, the Mifflin-St Jeor equation for metabolism, the U.S. Navy body fat method, Naegele’s rule for due dates and so on — and name the method on every page.
- Tested against known values. Each calculator’s logic is covered by automated tests that compare results with worked examples and reference values before anything is published.
- Explained in plain language. Every page includes the formula, a worked example and answers to common questions.
- Reviewed and updated. We review content periodically and correct anything that is out of date. If you spot an error, please tell us.
Our editorial standards
Every calculator page is written to answer a real question completely, not just to show a number. Each page includes:
- The method, named and explained — the formula, where it comes from and when it doesn’t apply.
- Worked examples that match the calculator’s default values, so you can follow every step.
- Reference tables calculated with the same formulas the calculator uses, so the tables and the tool agree.
- Practical guidance — how to measure inputs correctly, common mistakes, and what the result means for your decision.
- Sources — official bodies and published research such as the WHO, CDC, NICE, USDA, IRS, U.S. Department of Labor, ENERGY STAR and peer-reviewed studies, cited where they matter.
We don’t accept payment to include or rank products, and advertising never influences results or content.
How a calculator is made
- Research: we identify the standard method used by professionals — lenders, dietitians, veterinarians, builders — and the official rules that apply.
- Build and test: the calculation is written once, then checked by automated tests against published worked examples and independently computed values. The test suite runs before every update of the site.
- Edge cases: we test unusual inputs — leap years, month ends, zero interest rates, overnight shifts, very small and very large numbers — and show a clear message instead of a wrong answer.
- Write and review: the explanation is checked against the calculator so every example and table matches what the tool produces.
- Maintain: figures that change over time, such as tax rates, wage bases, minimum wages and benefit amounts, are reviewed on a regular schedule — at least every January and July, when most changes take effect.
Corrections
If you believe a result or explanation is wrong, please contact us with the page address and the values you used. We investigate every report, fix confirmed errors promptly and update the review date on the page.
Your privacy
All calculations happen in your browser. The numbers you enter are not sent to our servers or stored. See our privacy policy for details about cookies and advertising.
How the site is funded
CalcFinch is free to use and supported by advertising. Ads never influence our calculations or content.
Important note
Our calculators provide estimates for informational and educational purposes. They are not financial, medical, tax or legal advice. Please read our disclaimer.