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 publishes browser-based planning tools with visible assumptions, deterministic formulas and automated checks for the core math. The tools have not been independently reviewed by a financial or tax professional.

Each calculator runs in your browser using deterministic formulas. The core math library has automated regression tests, and each calculator page now links to its assumptions and source notes. Tests reduce mistakes; they are not a substitute for independent professional review.

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

PlainSums is an independent calculator publisher. We do not claim named editorial, tax or financial credentials that we cannot verify. Spotted a mistake or have a calculator you'd like to see? We'd genuinely like to hear it via our contact page.