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BMR Calculator
Your basal metabolic rate: the energy your body uses at complete rest, before you move at all.
The short answer
Your basal metabolic rate is roughly what you would burn lying still all day. For most people it is the largest single part of daily energy use, and it is an input to your calorie target rather than a target itself.
- Mifflin-St Jeor is used when body fat is unknown, Katch-McArdle when you supply a real measurement.
- Eating at your BMR means eating well below what you burn, because you are not lying still all day.
- Your calorie target is floored at the higher of your BMR and an absolute minimum.
- 1. About you
- 2. Activity
- 3. Goal
About you
These four details set your baseline. Metric units, since this is built for Australia.
years
cm
kg
If you know it from a DEXA or InBody scan, this makes the estimate more accurate. Leave it blank if you are guessing.
%Two quick checks
If either applies to you, generic calorie targets are the wrong tool and we will point you somewhere better instead.
What BMR is, and what it is not
Your basal metabolic rate is roughly what you would burn lying still all day: breathing, circulating blood, maintaining tissue, keeping your brain running. For most people it is the single largest part of daily energy use.
It is not a target. Eating at your BMR is eating well below what you burn, because you are not lying still all day. BMR is an input to the calculation, not an answer to how much to eat.
The two equations, and which one you get
If you do not give a body fat percentage, this calculator uses Mifflin-St Jeor, which works from your height, weight, age and sex. It is the standard choice when body composition is unknown.
If you do give a body fat percentage, it switches to Katch-McArdle, which works from your lean mass. That is the better equation when the figure is real, because two people at the same weight with very different body composition genuinely have different resting energy needs.
Only enter body fat if it came from a DEXA or InBody style scan. A guessed figure makes the estimate worse than leaving it blank, because it replaces a decent population estimate with a bad individual one.
Why your calorie target never goes below your BMR
Whatever goal you pick, your calorie target is floored at the higher of your BMR and an absolute minimum of 1500 calories for men or 1200 for women. That constraint is a safety limit, not a nutritional recommendation.
It exists because the arithmetic of a percentage deficit applied to a small maintenance figure can produce a number nobody should be eating, and a calculator that will hand you that number on request is a badly built calculator.
How these numbers are produced
Every figure on the results page comes from a fixed calculation, not from an AI guess. The same answers always produce the same numbers, which is why you can come back next month, enter the same details, and get the same targets.
An AI model writes the explanation you read underneath the numbers. It is given the figures after they have been calculated and it is not allowed to change them, recalculate them, or quote a figure the calculation did not produce.
- Resting energy is estimated with the Mifflin-St Jeor equation, or the Katch-McArdle equation if you tell us your body fat percentage, which is the more accurate of the two when that figure is known.
- Your activity multiplier comes from your weekly training sessions and how physical your work day is. The scale runs from 1.2 for sedentary to 1.9 for very high activity.
- We deliberately lean conservative on activity. Overestimating maintenance is the most common failure in consumer calculators, and it quietly makes every goal harder.
The limits built into this calculator
A calorie target handed to a stranger needs guardrails, so several are built in and cannot be overridden.
- Fat loss is capped at 1% of your bodyweight per week. Faster than that is not a setting you can choose here.
- Your calorie target never drops below the higher of your estimated resting energy and an absolute floor of 1500 calories for men or 1200 for women.
- There are no goal weight projections and no "you will reach X by this date" timelines, because those numbers are not knowable and they set people up to feel they have failed.
- If your details fall outside what a general calculator should answer, it stops and points you to a doctor or an Accredited Practising Dietitian instead of producing a number anyway.
What this calculator is not
This is general information. It is not personalised dietary advice and it is not medical advice. It cannot see your blood work, your training history, your medication or your relationship with food.
If you are managing a health condition, if you are pregnant or breastfeeding, if you have a history of disordered eating, or if you simply want targets built around your actual situation, speak to a doctor or an Accredited Practising Dietitian. That is a better use of your time than any calculator.
Common questions
Should I eat my BMR to lose weight?
No. Your BMR is what you burn at rest, so eating at it means eating well under what you actually burn once you include work, walking and training. Use your calorie target instead, which already accounts for all of that.
Which BMR formula is more accurate?
Katch-McArdle is generally the better choice when you have a real body fat measurement, because it works from lean mass. Without that measurement, Mifflin-St Jeor is the more reliable of the two. This calculator picks automatically based on whether you supplied the figure.
Can I increase my BMR?
Lean mass is the part of the equation you have meaningful influence over, and building it takes resistance training and enough protein and calories over a long period. The change is real but modest, and it is measured in months and years rather than weeks.
Why does age lower my BMR?
Both equations include age, and resting energy tends to decline over time, partly through loss of lean mass. That is why the same height and weight returns a lower figure at 55 than at 25.
