About PlainSums

PlainSums exists to make everyday money decisions clearer. Most finance calculators hand you a single number with no explanation. We do the opposite: every result is an itemized statement that shows exactly how the figure was built, so you can trust it and learn from it.

How our calculators are built

PlainSums' calculators are built and reviewed by writers with backgrounds in lending, financial planning and data. Every formula is documented and unit-tested.

Each calculator runs entirely in your browser using documented, openly-tested formulas — the same standard amortization, compound-interest and annuity math used across the finance industry. Our math library is covered by automated tests so the numbers stay correct as the site grows.

Our principles

Free and accessible to everyone. No account required. Nothing you type is stored or sent to a server. Clear over clever — we'd rather show the working than impress you. And we are always explicit that these tools are for education and planning, not personalized financial advice.

Who writes this

The PlainSums Editorial Team — Personal finance writers & analysts. Spotted a mistake or have a calculator you'd like to see? We'd genuinely like to hear it via our contact page.