CalcNow

About CalcNow

Twenty-eight free, browser-only calculators with the math and references behind them.

CalcNow is a collection of 28 free online calculators covering finance, health, unit conversion, and everyday math. Every tool runs entirely in your browser using JavaScript — your inputs are never sent to a server, never logged, and never persisted after you close the tab. There is no sign-up, no paywall, and no usage limit.

What makes CalcNow different

  • Each calculator ships with the math. Every page includes the full formula, three worked examples, common misconceptions, and references to the primary source the formula comes from — Mifflin-St Jeor (1990) for BMR, the WHO/CDC adult cut-offs for BMI, the standard amortization equation for mortgages, and so on.
  • Browser-based and private. Calculations run client-side. Your weight, salary, mortgage details, health metrics — none of it leaves your device.
  • No sign-up, no limits. Use any calculator any number of times on any device.
  • Cited against primary sources. Finance content references CFPB, IRS, Federal Reserve (FRED), and FHFA. Health content references WHO, CDC, NIH, and the original equation papers. Unit conversion references NIST SP 811 and the BIPM SI Brochure.

Our four calculator categories

  • Finance (10 tools) — mortgage, loan, auto loan, compound interest, ROI, salary, tip, discount, margin/markup, and rent-vs-buy.
  • Health & Body Composition (5 tools) — BMI, BMR, TDEE, body fat percentage, and age.
  • Unit Conversion (8 tools) — Fahrenheit-Celsius, inch-cm, pound-kg, MPG, cooking measures, shoe sizes, time between dates, and a multi-purpose converter.
  • Everyday (5 tools) — date, percentage, password generator, GPA, and age difference.

Editorial approach

CalcNow content is researched, written, and reviewed by three small editorial teams — one for finance, one for health and body composition, and one for unit conversion and everyday tools. We are not licensed financial advisors, medical professionals, or accountants, and CalcNow does not provide individualized financial, medical, or legal advice. The tools implement the standard published equations correctly so you can have an informed conversation with a qualified professional for personal decisions.

Each calculator page surfaces the limitations of its underlying method. BMI does not measure body fat. Mifflin-St Jeor estimates BMR within ±10%. The U.S. Navy body-fat method is less accurate at the extremes. We make those caveats explicit because honest tools beat confident ones.

Privacy and ads

CalcNow does not collect personally identifiable information. We use Google Analytics for aggregate traffic measurement and Google AdSense for advertising; both are governed by Google's Consent Mode v2, which means no analytics or ad cookies are set until you accept the cookie banner. See our Privacy Policy for the full breakdown.

Browse the full list on All Calculators or read our in-depth guides.