Is the BMR calculator free?
Yes. It is completely free to use, with no signup, no account, and no paywall.
Are the results medical advice?
No. The output is a general estimate built from standard formulas and population averages. For decisions about your health, diet, or training, check with a doctor or registered dietitian.
Does it stay local?
Yes. The height, weight, and other details you enter are processed entirely in your browser and never uploaded.
Should I eat my BMR?
No. BMR is what you burn at complete rest. Eating to it, on top of a normal day of moving around, is a large and usually unintended deficit. Multiply by an activity factor first, which is what the TDEE calculator does.
Why does the male formula add 5 and the female one subtract 161?
Those constants come straight out of the regression Mifflin and St Jeor fitted to their measured subjects. The 166 calorie gap between them is the equation's way of accounting for the average difference in lean body mass at the same height, weight, and age.
How accurate is it?
It gets within about 10 percent of measured resting energy expenditure for most healthy adults, and it is the most accurate of the common predictive equations. It is still a prediction from four numbers, not a measurement.
Is it better than Harris-Benedict?
For most people, yes. Harris-Benedict dates from 1919 and tends to overestimate, particularly in people with more body fat. Mifflin-St Jeor was fitted to a more representative modern population, which is why it is the recommended default.
Does BMR fall as I lose weight?
Yes, and the formula shows it: BMR is proportional to weight, so 10 kilograms lost takes roughly 100 calories a day off the estimate. This is one reason weight loss slows down over time even when nothing about the diet changes.