How we calculate

Every calculator on this site comes with an open calculation memo: we show the formula, the assumptions it relies on, and the source of each number. Nothing is hidden behind a black box.

1. Transparent formulas, not black boxes

Our tools are built on established financial mathematics — compound interest, the SAC and Price amortization systems, present and future value, internal rate of return (IRR), the Rule of 72, and the 4% rule (Bengen, 1994). These are the same methods used by finance professionals everywhere. Redo any of them by hand or in a spreadsheet and you get the same result we show.

2. The calculation runs in your browser

All logic runs locally in JavaScript, on your own device. The values you type are never sent to a server, never stored, and never shared. That means privacy by default and instant results — no waiting, no accounts, no tracking of your numbers.

3. Where the reference data comes from

For rates and indices that change over time, we check the figures against official sources before they go live, and we mark the reference year (2026) in the tool. The primary references we rely on for an international audience are:

Topic	Official source
Interest rates & monetary policy	U.S. Federal Reserve
Taxes & tax brackets	U.S. Internal Revenue Service — IRS
Markets & securities	U.S. Securities and Exchange Commission — SEC
Inflation & economic data	OECD
Safe withdrawal / retirement research	Bengen (1994), "Determining Withdrawal Rates Using Historical Data"

4. How we keep it up to date

When a rule or index changes, we update the affected calculator and date the change. We do not scrape third-party news feeds or repackage figures we can't trace back to an official source.

5. An honest disclaimer

Who maintains this

Content is maintained by Vinicius Fonseca, who reviews the formulas and the sources. Found a discrepancy? Email contact@calculatorsmoney.com.