About fcalculator
fcalculator is an independent website with 38 financial calculators for people in the United States, the United Kingdom and Europe. Each one shows not just a number but how it was reached: a chart, a full schedule, a plain explanation and the sources behind it.
Why we built it
Most calculators give you one figure and stop. A monthly payment on its own does not tell you that two thirds of it is interest, that a longer term costs more in total, or that the rate you typed is a point above what lenders charge this week. We wanted calculators that answer the next question too, without sign-ups, pop-ups or a sales pitch at the end.
How the calculators are built
- Standard formulas, stated on the page. Loan, mortgage and savings calculators use the standard amortization and compound-interest formulas. Every page shows the formula and a worked example you can check by hand.
- Official tax rules. US federal tax figures come from the IRS revenue procedure for the year (for 2026, Rev. Proc. 2025-32), UK figures from GOV.UK, German payroll tax from the Federal Ministry of Finance's official calculation rules. Our German calculator matches the ministry's published test cases to the cent.
- Live, sourced data. Mortgage rates, central bank rates, inflation, exchange rates and debt figures are fetched several times a day from Freddie Mac, the Federal Reserve Bank of St. Louis (FRED), the European Central Bank, the Bank of England, Eurostat, the ONS and the U.S. Treasury. Each page names its source and the date of the figure.
- Checked before publishing. Every calculator is tested against hand-worked examples before it goes live, and the examples in our explanations are recalculated whenever figures change.
Keeping it current
Tax brackets and allowances change every year. We update US figures when the IRS publishes the new year's numbers each autumn and UK figures for each April tax year. Every calculator shows the date it was last updated at the top of the page.
Your data
The calculators run in your browser. The numbers you type are not sent to our server or stored by us; if you share a result, the inputs travel in the link you choose to share. The site is funded by advertising. Details are in our privacy policy.
What we are not
We are not a bank, lender, broker or financial adviser, and we are not paid to recommend any product. Results are estimates for planning and learning. For decisions about your own money, taxes or legal position, speak to a qualified professional.
Found a mistake?
Tell us on the contact page. Include the page and the numbers you used. Confirmed errors are fixed and the page's update date changes when we do.
More than money
fcalculator started as a general calculator site, and the older tools are still here: countdowns, time zones, unit converters and health calculators. You will find them under More tools.