Every calculation is a tested function
The maths behind each tool lives in a separate library from the website itself. Each calculator is a pure function — the same inputs always produce the same output, with no hidden state, no rounding applied for presentation before the result is computed, and no network call in the middle. That is a deliberate constraint rather than an implementation detail: it is what makes a result reproducible, and it is why the formula shown on the page is the formula that actually ran.
Each function is covered by unit tests that check it against worked examples, boundary conditions, and cases where the naive implementation is wrong — zero interest rates, single-period terms, payments that never amortise. Those tests run on every change before anything reaches this site.
Your inputs never leave your browser
Calculators run entirely on your device. Salary, balances, debts, and savings are never transmitted to us, never stored, and never logged — so there is nothing on our side to leak, sell, or hand over. This is also why there is no account to create: we would have nothing to put in it.
Assumptions are stated, not buried
Any calculator that models the future has to assume something — a rate of return, an inflation figure, a compounding frequency, a tax treatment. Those assumptions are printed on the page next to the result, with the value used and where it came from, rather than being folded silently into a single number. Where a reasonable person would choose differently, the assumption is an input you can change.
Where the data comes from
Rate and market figures come from primary sources — the issuing agency or exchange — rather than aggregators, and each page names the source it used. The About page lists them in full.
What we do not claim
This is the part most sites leave out, so it is stated plainly:
- No financial professional has reviewed this content. The calculations are tested for mathematical correctness. That is a different thing from a licensed adviser confirming the approach is right for you, and we do not claim the second.
- Nothing here is personalised advice. The site does not know your circumstances, and a calculator cannot weigh them.
- No calculator recommends a product. A result is arithmetic. Nothing on a calculator page is an affiliate link, and no number anywhere on this site changes based on who pays us.
- Projections are arithmetic, not forecasts. A compound-growth figure shows what a rate would produce if it held. It is not a prediction that it will.
Corrections
If a number here is wrong, we want to know and we will fix it. Report it through the contact page with the page and the inputs you used. Errors in the maths are corrected as a priority, and the fix ships with the test that would have caught it.
Who writes this
Roland Balabekyan. Builds and maintains FigureBetter. Wrote the calculation engines behind every tool on the site — each one a pure function covered by unit tests — and the pages that show the formula and the sources behind every number. More on the About page.