Are these health calculators free?

Yes. No account, no email signup, no premium tier. Enter your numbers and the result appears immediately.

Is my personal data (weight, age, body fat) sent to a server?

Every calculator runs as JavaScript inside your browser. All processing is local — the numbers you enter are used only for the calculation in that browser tab.

How accurate are these calculators?

Each calculator uses an established, peer-reviewed formula. BMI follows the WHO classification, TDEE uses Mifflin-St Jeor (1990), body fat uses the US Navy circumference method, one rep max uses Epley and Brzycki, heart rate zones use the Tanaka formula (2001). These are the same formulas used by clinicians and fitness coaches, but they are estimates, not diagnoses.

Should I use these results to make medical decisions?

No. A BMI in the overweight range, an unexpected body fat percentage, or any other surprising result should be discussed with a doctor or a qualified health professional. The calculators give you a starting number, not advice.

Why does BMI sometimes feel wrong?

BMI is a ratio of weight to height squared. It doesn't account for muscle mass, bone density, or body composition. A very muscular person can register as overweight by BMI while having low body fat. For a more nuanced view, combine BMI with the body fat calculator.

Do I need to enter metric units, or does imperial work too?

Both. Each calculator has a toggle between metric (kg, cm) and imperial (lb, ft + in). The math is identical, the conversion is done internally and exactly.

Do these calculators work offline?

After the first visit, yes. The whole site is statically exported. Once cached, every calculator works without an internet connection. Useful in a gym with bad Wi-Fi.

Why doesn't the site offer to save my history?

Storing your weight over time would mean writing personal health data to your device, which we don't want to do without explicit consent. If you want to track results, copy the numbers into a notes app or a dedicated tracking app you trust.

Free health calculators, online, in-browser

A set of health and fitness calculators that run entirely in your browser. Calculate your Body Mass Index (BMI), Total Daily Energy Expenditure (TDEE), body fat percentage, one rep max for strength training, ideal weight range, and heart rate training zones.

All calculators use established scientific formulas and run as JavaScript in your browser tab. All calculations happen in JavaScript running locally on your device. Results are for informational purposes and do not constitute medical advice.

Read the complete health tools guide

Lean body mass calculator

Estimate lean body mass, fat mass, and implied body fat percentage using the Boer formula.

Pregnancy due date calculator

Calculate your estimated due date from your last period or conception date. Includes gestational age and trimester.

BMI calculator

Calculate your Body Mass Index in metric or imperial units. Instant WHO category result.

Calorie / TDEE calculator

Calculate your Total Daily Energy Expenditure and calorie targets for weight loss or gain.

Body fat calculator

Estimate body fat percentage using the US Navy circumference method. No calipers needed.

One rep max calculator

Estimate your 1RM for any lift using Epley and Brzycki formulas. Includes a full percentage table.

Ideal weight calculator

Find your ideal weight range using Hamwi, Devine, and BMI-range formulas for your height.

Heart rate zone calculator

Calculate your maximum heart rate and 5 training zones using the Tanaka formula.

How in-browser health calculators work

BMI, TDEE, body fat percentage, and the rest are formulas. They are simple enough to evaluate directly in JavaScript on the device, without any server involvement. You enter the numbers into a form on the page, the script runs the formula, and the result appears. Close the tab and the inputs are gone from memory.

Results are estimates from population-level formulas (WHO BMI categories, Mifflin-St Jeor BMR, Hodgdon-Beckett body fat, Tanaka max heart rate, and so on, all cited on the individual tool pages). They are not a substitute for clinical assessment. Discuss anything that matters with a healthcare provider who can interpret the numbers in context.

How the calculators work

Each calculator implements a published formula directly in JavaScript. The BMI calculator divides weight in kilograms by height in metres squared and looks up the WHO category for the result. The TDEE calculator applies the Mifflin-St Jeor basal metabolic rate equation and multiplies by the activity factor you choose. The body fat calculator uses the US Navy circumference method (Hodgdon & Beckett, 1984), which estimates body fat from neck, waist, and (for women) hip measurements together with height.

The one rep max calculator combines the Epley and Brzycki formulas. The heart rate zone calculator uses the Tanaka equation (208 minus 0.7 times age) for maximum heart rate, then computes five training zones as percentages of that value, with the Karvonen formula available if you supply your resting heart rate.

All math is done in standard JavaScript with no library beyond the language itself. The formulas are simple enough that there is nothing to outsource to a server, and the privacy benefit of keeping the numbers local is real.

In-browser health calculators vs the alternatives

Approach	Privacy	Tracks over time	Best for
In-browser (this site)	All local	No	One-off calculations, sanity checks
Online health calculator sites	Server-side	No	Quick lookups when privacy is not a concern
Fitness tracking apps	Cloud sync	Yes	Long-term tracking, integration with wearables
Doctor or clinician	Medical confidentiality	Yes (in your record)	Actual health advice and diagnosis

The four options answer different questions. Use the in-browser calculators here when you want a quick number without sharing your biometric data. Use a fitness app if you want to track changes over months. Talk to a clinician if you want medical advice.

When to use these tools

Setting weight or nutrition goals? Combine the BMI calculator with the TDEE and calorie target estimator to plan a realistic surplus or deficit.
Curious about body composition rather than just total weight? Estimate body fat percentage with tape measurements, or compute lean body mass using the Boer formula.
Programming gym sessions? Predict your strength ceiling with the one rep max calculator and dial in cardio intensity through the heart rate zone calculator.
Looking for a healthy weight range? The ideal weight calculator compares Hamwi, Devine, and BMI-range estimates for your height.
Expecting? Map out a timeline with the pregnancy due date calculator, which shows gestational age and trimester.

Frequently asked questions

Are these health calculators free?: Yes. No account, no email signup, no premium tier. Enter your numbers and the result appears immediately.
Is my personal data (weight, age, body fat) sent to a server?: Every calculator runs as JavaScript inside your browser. All processing is local — the numbers you enter are used only for the calculation in that browser tab.
How accurate are these calculators?: Each calculator uses an established, peer-reviewed formula. BMI follows the WHO classification, TDEE uses Mifflin-St Jeor (1990), body fat uses the US Navy circumference method, one rep max uses Epley and Brzycki, heart rate zones use the Tanaka formula (2001). These are the same formulas used by clinicians and fitness coaches, but they are estimates, not diagnoses.
Should I use these results to make medical decisions?: No. A BMI in the overweight range, an unexpected body fat percentage, or any other surprising result should be discussed with a doctor or a qualified health professional. The calculators give you a starting number, not advice.
Why does BMI sometimes feel wrong?: BMI is a ratio of weight to height squared. It doesn't account for muscle mass, bone density, or body composition. A very muscular person can register as overweight by BMI while having low body fat. For a more nuanced view, combine BMI with the body fat calculator.
Do I need to enter metric units, or does imperial work too?: Both. Each calculator has a toggle between metric (kg, cm) and imperial (lb, ft + in). The math is identical, the conversion is done internally and exactly.
Do these calculators work offline?: After the first visit, yes. The whole site is statically exported. Once cached, every calculator works without an internet connection. Useful in a gym with bad Wi-Fi.
Why doesn't the site offer to save my history?: Storing your weight over time would mean writing personal health data to your device, which we don't want to do without explicit consent. If you want to track results, copy the numbers into a notes app or a dedicated tracking app you trust.