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About CalcRun

Financial calculators that show their working.

Who built this

CalcRun is built by Jonathan, an ACA-qualified accountant with experience across UK, US, and Australian tax systems. The site exists because most online calculators are either ad-heavy, outdated, or won't show their working. This one does.

Every formula is documented, every tax rate is sourced from official data (HMRC, IRS, SSA), and every calculation runs in your browser — nothing is sent to a server. If you find an error, email me and I'll fix it.

What we build

CalcRun offers 44 tools across six categories: savings and growth calculators, debt and loan tools, income and tax planning, economic indicators, developer utilities, and file converters. Every financial calculator includes interactive charts, a year-by-year breakdown table, and educational content explaining the underlying formulas.

UK tax calculators use 2025/26 HMRC rates. US tax calculators use 2025 IRS brackets. Rate-dependent tools display their data sources and the date we last verified them.

How privacy works

All calculations run client-side in your browser. The numbers you type into a calculator never leave your device — we cannot see them. We use Google Analytics for aggregate traffic data (page views, country). We do not sell data or run tracking pixels for ad networks. Read our privacy policy for full details.

How it's funded

Some calculator pages include affiliate links to financial products. If you click through and open an account, we may earn a commission at no extra cost to you. Calculator results are never affected by affiliate partnerships — the same formula runs regardless of which links appear on the page. See our affiliate disclosure for the full list of partners.

Editorial standards

  • Cited sources. Tax rates, thresholds, and pension figures link to the official government source (GOV.UK, IRS, SSA).
  • Last-checked dates. Every rate-dependent calculator shows when we last verified its data against official sources.
  • Formula transparency. Each calculator identifies its calculation method so you can verify the maths independently.
  • Corrections. If you find an error, email hello@calcrun.com and we'll fix it within 24 hours.

Not financial advice

CalcRun provides educational tools, not personalised financial advice. Calculators use general formulas and published tax rates — they cannot account for your complete financial situation. For decisions about investing, tax planning, or pensions, consult a qualified financial adviser.