About RiverMath
RiverMath is built for the moment you need a fast, reliable number without creating an account, clicking through pop-ups or handing over your email address. Type your numbers and see the answer immediately.
What you can calculate
The collection covers five everyday areas: body and training, money and investing, work and pay (including 2026 Polish employment and B2B tax models), home energy (solar PV, heat pumps, G11/G12 tariffs) and quick math, physics and unit converters.
Jump straight to a category:
How it works
Every formula runs directly in your browser once the page loads. There is no sign-in and no server round-trip to compute a result. Recent results are kept in your browser’s local storage by default. Body, pregnancy, ovulation and breathalyzer readings never leave your device.
Who it is for
Anyone who values clear arithmetic: freelancers comparing B2B tax regimes or adding VAT, homeowners sizing solar panels or overpaying a mortgage, runners checking 10K pace splits, and students verifying homework equations.
What this is not
All calculators provide educational and planning estimates. They do not replace a medical diagnosis, a binding bank quote, an official payslip, or formal tax advice from a certified accountant.
Sister project: Longseries
Historical time series and downloadable statistical datasets live on our sister site, Longseries. RiverMath runs the equations — Longseries archives the data.
Common questions
- Is RiverMath completely free?
- Yes. All 145 calculators are free to use in your browser with no paywall, subscriptions or registration.
- Do you store the numbers I enter?
- All calculations run locally in your browser. A copy of a result is sent to the server only if you manually enable sync on the History page (accessible solely to the site owner via PIN). Body, pregnancy, ovulation and breathalyzer tools are hard-blocked from ever syncing to the server.
- Are the salary, tax and loan figures official?
- No. They are simplified planning models. Official tax filings, credit agreements and payslips are issued by tax offices, banks, accountants and employers.
- Which languages are supported?
- English (/en), Polish (/pl) and German (/de). Poland-specific tax, labour and energy calculators remain accessible in all three languages under Poland’s flag.
- Can I share a calculation with someone else?
- Yes — use the buttons below any result to copy the formatted output or a direct link with your inputs pre-filled.