BMR Calculator
Free BMR calculator. Mifflin-St Jeor or Harris-Benedict, imperial or metric. Find resting calories burned per day. No signup.
What BMR means
Basal metabolic rate (BMR) is the number of calories your body burns at complete rest to stay alive — breathing, circulating blood, holding body temperature, and running every cell. It is the floor under your daily energy needs and usually the largest single share of the calories you burn. This calculator estimates it from age, sex, weight, and height using two established equations, and shows the sedentary calorie floor that follows from it.
How the BMR calculator works
- Mifflin–St Jeor (the default): male 10 × kg + 6.25 × cm − 5 × age + 5; female 10 × kg + 6.25 × cm − 5 × age − 161.
- Harris–Benedict (revised 1984): a legacy equation you can select to compare against.
- Average: the mean of the two formulas, if you want a middle estimate.
- Imperial or metric input is converted to kilograms and centimetres before the equation is applied, then the answer is rounded.
- It also reports the calories you would burn if sedentary (BMR × 1.2), which is a useful floor for daily intake.
A worked example
A 30-year-old male, 170 lb, 67 inches tall, using the default Mifflin–St Jeor formula:
| Step | Calculation | Result |
|---|---|---|
| Weight in kg | 170 × 0.45359 | 77.1 kg |
| Height in cm | 67 × 2.54 | 170.2 cm |
| Mifflin–St Jeor | (10 × 77.1) + (6.25 × 170.2) − (5 × 30) + 5 | 1,690 kcal |
| Harris–Benedict | 88.362 + (13.397 × 77.1) + (4.799 × 170.2) − (5.677 × 30) | 1,768 kcal |
| Average of both | (1,690 + 1,768) ÷ 2 | 1,729 kcal |
| Calories if sedentary | 1,690 × 1.2 | 2,028 kcal |
Note how far apart the two equations can sit — roughly 80 kcal here. That spread is normal. These are population estimates, not measurements of you.
Which formula should you use?
| Formula | Result here | Notes |
|---|---|---|
| Mifflin–St Jeor | 1,690 kcal | Most widely validated; the default |
| Harris–Benedict (1984) | 1,768 kcal | Historic; tends to read a little higher |
| Average | 1,729 kcal | Splits the difference between them |
From BMR to daily calories
BMR is not your daily burn — it is only the at-rest layer. Multiply it by an activity factor, from roughly 1.2 for sedentary up to 1.9 for a physical job plus hard training, to reach total daily energy expenditure. In this example, 1,690 kcal at rest becomes about 2,620 kcal at moderate activity. That total is the number that actually decides whether you lose or gain weight.
Common mistakes
- Eating at BMR to lose weight. BMR is not a safe intake target; it ignores daily activity and usually sits far below maintenance.
- Treating one formula as “wrong.” Both are estimates. A gap of around 5% between them is expected, not an error.
- Assuming BMR is fixed. It falls as you lose weight and rises with muscle mass. Recalculate after a meaningful change.
- Confusing BMR with RMR. Resting metabolic rate is measured under looser conditions and reads slightly higher; in daily use the two are close.
Frequently asked questions
What is the difference between BMR and RMR?
BMR is measured under strict conditions: after an overnight fast, at complete rest, soon after waking. RMR is measured under ordinary resting conditions and typically reads 5–10% higher. Most calculators — including this one — apply BMR equations to both jobs because the practical difference is small.
What raises or lowers BMR?
Muscle mass raises it; fat mass contributes less per kilogram. It also falls with age and during aggressive dieting, and rises temporarily with fever, stress, or a large food surplus. Building muscle is the slowest but most durable lever you control.
Should I eat my BMR calories?
Only if that happens to match a healthy rate of loss, which is rare. Eating at BMR usually means a very steep deficit. Set intake relative to your total expenditure instead — the TDEE calculator handles that step.
Why does a smart scale give a different BMR?
Scales estimate body composition and then feed it into a formula; so does this tool. Neither measures metabolism directly, and both carry real error. Use one consistent method and watch the trend rather than trusting any single number.
Once you have a BMR you trust the ballpark of, pair it with an estimate of body fat to see how much of your weight is lean tissue — the part that drives this figure.