How it works
- 01
Enter your measurements
Age, sex, height and weight. Body fat is only needed for Katch-McArdle.
- 02
Pick an activity level
This is the biggest source of error. When in doubt, pick the lower of two.
- 03
Read the goal rows
Each row applies a fixed daily change to your maintenance figure.
How the estimate is built
The estimate runs in two stages. First comes the basal metabolic rate, the energy your body uses at complete rest. It is worked out from height, weight, age and sex. Mifflin-St Jeor is the default, because it has held up best against measured resting rates in adults. Harris-Benedict and Katch-McArdle are there for comparison. The second is useful if you know your body fat percentage.
That rate is then multiplied by an activity factor, from 1.20 for sedentary to 1.90 for heavy training. The multiplier is the largest source of error in the whole estimate. People routinely overrate their activity, and the gap between light and moderate is about 250 kcal a day. Pick the lower of two plausible options, then adjust from real results after two or three weeks.
- Formulas
- Mifflin-St Jeor, Harris-Benedict revised, Katch-McArdle.
- Accuracy
- About 10% either way. Metabolism varies between people.
- Deficit maths
- A kilogram of fat is about 7,700 kcal, so 500 a day is 0.45 kg a week.
- Stored data
- None. Values stay in the page and clear on reload.
Using the goal rows
Each goal row applies a fixed daily change to your maintenance figure. A 500 kcal deficit is the usual starting point for losing weight. It is large enough to show on a scale within a fortnight, and small enough to keep up. Deficits beyond roughly a quarter of maintenance tend to cost muscle rather than fat.
Maintenance is not fixed for life. It falls as body mass falls. A figure worked out at the start of a cut overshoots by a few hundred calories several kilograms later. Run it again every 4 to 5 kg.