Online Tool Store
· 4 min read
3 BMR Calculator Tools, Compared Honestly
Heshan Fernando
Co-founder & COO
You want to know how many calories your body burns at complete rest — before any activity, exercise, or digestion is factored in.
The formulas involved aren’t controversial, but different calculators default to different equations without always explaining which one they’re using or why it might differ from another site’s result.
How to judge a BMR calculator tool
Names its formula. Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle give different results — a calculator should say which one produced your number.
Offers more than one formula. Comparing formulas side by side helps you see how sensitive the estimate is to the method used.
Is honest about accuracy. BMR from a formula is an estimate, not a lab measurement — a calculator that says so plainly is being straight with you.
Free tier gives the real number. No signup for a basic calculation.
The comparison
| Tool | Best for | Free tier | Watch out |
|---|---|---|---|
| Calculator.net | Three formulas including Katch-McArdle | Free, no signup | States a notable unknown variance even with rigid formulas |
| NutriAdmin | Four formulas, side-by-side comparison | Free, no signup for the calculator | Promotes a paid software trial alongside the tool |
| The Calculator Site | Simple three-formula comparison | Free, no signup | Doesn’t account for lean body mass differences |
| BMR Calculator | Mifflin-St Jeor, Harris-Benedict, Katch-McArdle side by side | Free, no signup | No Schofield formula option |
Facts checked August 2026; tools change their plans.
Calculator.net
Calculator.net’s BMR tool offers Mifflin-St Jeor, revised Harris-Benedict, and Katch-McArdle formulas, and is upfront that research shows roughly 26% unknown variance between individuals even with rigid formulas, recommending calorimetry for anyone who needs precision.
It isn’t for someone who wants a fourth formula option like Schofield — it sticks to the three most commonly cited equations.
NutriAdmin
NutriAdmin supports four formulas — Mifflin-St Jeor, Harris-Benedict, Katch-McArdle, and Schofield — with a comparison view, and clearly lists what BMR formulas don’t account for, including thermic effect of food, activity, and medical conditions.
It isn’t for someone avoiding promotional content — the calculator sits next to ongoing prompts for a 14-day trial of NutriAdmin’s paid nutrition software.
The Calculator Site
This calculator defaults to Mifflin-St Jeor with Harris-Benedict (both original 1919 and revised 1984) as alternatives, and explicitly notes that BMR calculations don’t factor in lean body mass, which matters for very muscular or overweight individuals.
It isn’t for someone who wants the Katch-McArdle formula, which adjusts for body fat percentage — that option isn’t offered here.
BMR Calculator
Our calculator runs Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle side by side from the same inputs, so you can see how the estimate shifts by formula, all calculated in your browser.
A real limitation: it doesn’t include the Schofield equation, which some clinical settings use — for that specific formula, you’d need a tool like NutriAdmin.
Which one to pick
If you want three common formulas compared side by side with no signup, use our BMR Calculator.
If you specifically need the Schofield formula alongside the others, use NutriAdmin.
If you want the clearest statement of what BMR calculations can’t capture, use Calculator.net.
If you want a simple, ad-light comparison of Mifflin-St Jeor against both Harris-Benedict versions, use The Calculator Site.
How to do it with BMR Calculator
- Open the BMR Calculator.
- Enter your age, sex, height, and weight.
- Compare your BMR across the Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle formulas, side by side.
Browse the full tools directory for more free, browser-based health calculators.
You might also need
BMR is your calorie burn at complete rest; most days you’re not at complete rest. Our TDEE Calculator takes your BMR and multiplies it by an activity factor to estimate your total daily calorie burn.
Frequently asked questions
Is there a free BMR calculator that doesn’t need an account?
Yes. Our BMR Calculator and all three alternatives here calculate your BMR without requiring signup.
Which BMR formula is most accurate?
Mifflin-St Jeor is widely cited as the most accurate common formula for the general population, though Katch-McArdle can be more accurate for people who know their body fat percentage, since it factors in lean body mass directly.
Why do different BMR calculators give different results?
Different calculators often default to different formulas — Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle all use slightly different equations and can produce results that vary by a few hundred calories for the same person. The original Harris-Benedict equation dates to 1919 and has been revised multiple times since, which is part of why the numbers diverge.
Final thought
BMR from any formula is an estimate — comparing two or three formulas side by side, rather than trusting a single number, gives a more honest sense of the range your actual resting metabolism likely falls in.