Free fitness calculators
that actually help
Every formula published, every caveat stated. No sign-up, and nothing you type leaves your browser.
Core calculators
Start here. Each one shows the equation it used and how far wrong it can be.
TDEE Calculator
Calculate your total daily energy expenditure with the Mifflin-St Jeor equation. Free TDEE calculator with the full formula, worked examples and accuracy caveats.
BMR Calculator
Calculate your basal metabolic rate with two published equations, and see exactly what your resting metabolism pays for.
Macro Calculator
Get your daily protein, carbohydrate and fat targets in grams, with protein set from bodyweight first — the order that actually matters.
Body Fat Percentage Calculator
Estimate your body fat percentage from tape measurements using the US Navy method, with honest error margins and measuring technique.
Ideal Weight Calculator
Four published ideal weight formulas shown as a range, plus what they cannot see and what to use instead.
One Rep Max Calculator
Estimate your 1RM from any set, with all three formulas compared and a percentage table for programming.
Calories Burned Calculator
Work out the calories burned in any activity from its MET value and your bodyweight — including the gross-versus-net correction most apps get wrong.
More calculators
Newer tools, same approach.
BMI Calculator
Calculate your BMI and, more usefully, your waist-to-height ratio — the measurement that actually reflects health risk.
Lean Body Mass Calculator
Calculate your lean body mass and normalised FFMI using three published equations, or directly from a body fat percentage.
Weight Loss Timeline Calculator
How long your goal weight will take at a rate that preserves muscle, projected week by week with a falling TDEE.
Water Intake Calculator
Estimate your daily water needs from bodyweight, training volume and climate — and why the eight-glasses rule has no research behind it.
Reference tables
The lookup data behind the calculators, published in full — no inputs required.
MET Values Table
A searchable MET (metabolic equivalent) table for 180+ activities, with calories burned per hour at 60, 70, 80, 90 and 100 kg bodyweight. Based on the Compendium of Physical Activities.
Protein Target Table
How much protein you need per day, in grams, for every bodyweight from 45 to 125 kg (100 to 275 lb) and six different goals — with the research behind each target.
BMR Formula Comparison
Six BMR equations side by side, with the full arithmetic, worked examples for the same person, and guidance on which formula to use for your body type.
Latest guides
Longer reads on what to do once you have your number.
Reverse Dieting: How to Come Off a Cut Without Regaining
Most diets do not fail during the diet. They fail in the fortnight afterwards, when a finished cut turns into no plan at all. Reverse dieting is simply having a plan for that fortnight — and it is less magical and more useful than its reputation suggests.
How to Estimate Your One Rep Max Without Testing It
Testing a true one rep max is risky, fatiguing, and costs you a week of training. Estimating it from a set you were going to do anyway costs nothing — provided you understand where the estimate goes wrong.
Body Fat Measurement Methods Compared (And Their Real Error)
Every method of measuring body fat is wrong. The useful question is not which one is right — it is which one is wrong in a consistent direction, because a consistent error still tracks change perfectly.
Which Activity Multiplier Should You Use? (Most People Pick Wrong)
Your BMR equation is accurate within about 10 percent. Then you multiply it by a number you chose from a dropdown based on a vibe. That single choice can swing your calorie target by 700 calories a day.
Why use MyBodyMath?
Every calculator here is a direct implementation of a published equation — no proprietary scores, no adjusted results. Each one names its source, states its margin of error, and tells you what to do next.
Free, private, and instant: your results are calculated in your browser and nothing is stored on our servers. See also: How We Calculate, editorial policy, about page.