Health & Fitness Calculators
The everyday health calculations that don't need an app subscription.
The health metrics people search for most — BMI, body-fat percentage, ideal weight range, daily calorie needs — are all one-formula answers. Fitness apps wrap them in gamified onboarding and monthly fees; they're just calculators.
Every tool here is a starting point, not a diagnosis. If a number surprises you, the next step is talking to a doctor or a certified professional, not doubling down on the calculator.
The Mifflin-St Jeor formula, applied cleanly. No app subscription, no gamified onboarding — just the number.
Open TDEE CalculatorBody composition
BMI, body-fat, and ideal-weight ranges.
- BMI CalculatorCalculate your Body Mass Index (BMI) in metric or imperial units. Shows category and healthy weight range for your height.
- Body Fat Calculator (US Navy)Estimate body fat percentage using the US Navy tape-measure method. Needs only waist, neck (and hip, for women), and height. Metric or imperial.
- Ideal Body Weight CalculatorEstimate ideal body weight (IBW) using the Devine, Robinson, Miller, and Hamwi formulas. Compares all four in metric and imperial, based on height and sex.
Calories & nutrition
Daily energy needs and cooking measurement conversion.
- TDEE CalculatorCalculate your Total Daily Energy Expenditure (TDEE) — the calories you burn per day. Includes BMR (Mifflin-St Jeor), activity multiplier, and cut / maintain / bulk targets.
- Cooking Measurement ConverterConvert cooking measurements between US customary (cups, tbsp, tsp, oz) and metric (ml, g). Volume and mass covered.
- Universal Unit ConverterConvert between units across 8 dimensions: length, mass, volume, time, area, digital storage, speed, and temperature. Instant, accurate, in your browser.
Milestones & timing
Age at any date, countdowns to a goal.
- Age CalculatorEnter a date of birth to see age in years, months, days, hours, minutes, and seconds. Optionally compute age at any past or future date.
- Age at Date CalculatorCalculate how old someone was (or will be) on a specific date. Shows years, months, and days plus totals in weeks and days. Handy for historical timelines and future planning.
- Date Difference CalculatorCalculate the number of days between two dates in three modes: total calendar days (with weeks / hours / years-months-days breakdown), working days (weekends excluded, custom holidays optional), or US business days (federal holidays excluded automatically with observed-day shifts).
- Countdown TimerCount down to any date and time, second by second. Add a label and share the URL — everything lives in the link, no login required.
Or reach for a broader tool
Third-party products that fit this use case. Our built-in tools cover the small technical jobs; these cover the bigger workflows around them. External links, hand-picked, not sponsored.
- MyFitnessPalFreemiumFood and calorie tracking with a large user database.
- Massive user-contributed food database (barcode scanning)
- Calorie + macro tracking
- Free plan is usable; Premium unlocks meal planning + no ads
Best for: People who want detailed food logging without building their own spreadsheet.Free · Premium from $19.99/moVisit MyFitnessPal - StravaFreemiumActivity tracking + social layer for runners and cyclists.
- GPS activity tracking (works from phone or watches)
- Segments (compare your time on a route against yourself and others)
- Free plan covers most needs; subscription adds heatmaps + route planner
Best for: Runners and cyclists who want a permanent record of their training + gentle peer accountability.Free · Subscription from $11.99/moVisit Strava - CronometerFreemiumNutrition tracker with a verified food database.
- Food data verified from USDA + NCCDB (not user-submitted)
- Tracks 82+ micronutrients (most trackers only show macros)
- Free version handles the essentials
Best for: People with specific nutrition targets (deficiencies, specific diets) where accurate data matters.Free · Gold from $9.99/moVisit Cronometer