Basal metabolic rate is the energy your body would burn if you stayed in bed all day — typically about 60–70% of a sedentary adult’s total daily energy expenditure. It is not TDEE. TDEE multiplies BMR by an activity factor that describes the rest of your life: walking, standing, fidgeting, and formal training. Confusing the two is how people eat a “maintenance” that is actually a large surplus, or cut to a number that is already below true rest. This page computes BMR with the Mifflin-St Jeor equation (1990), which validation studies generally treat as the most accurate general-population formula, and shows Harris-Benedict (original 1919, revised 1984) beside it so you can see why two websites disagree by 80–150 kcal. Mifflin-St Jeor for men is 10×weight(kg) + 6.25×height(cm) − 5×age + 5; for women the constant is −161 instead of +5. Harris-Benedict uses a different intercept and slightly different coefficients; it tends to run a little higher in many modern adults. After you have BMR, apply an activity factor between 1.2 (desk, little walking) and 1.9 (physical job plus hard training). Most desk workers who lift three times a week live near 1.375–1.55, not 1.9. Recalculate when body weight moves about 5 kg, when you change jobs or seasons, or when the scale disagrees with the math for three weeks. This is an educational estimate, not a lab measurement and not medical advice. Indirect calorimetry in a clinic beats any equation. StepDay will not measure BMR, but it will show whether your steps and workouts match the factor you just picked.
Compute rest, pick an honest factor, verify with the scale, recalculate when life moves.
Enter age, sex, height, and weight once. Read Mifflin-St Jeor as the default BMR and Harris-Benedict as the historical check. If they diverge by more than about 150 kcal, you are looking at coefficient differences, not a broken widget. Use Mifflin for planning unless a clinician or sport dietitian has a reason to prefer another equation. Do not average them into a fake third number.
BMR × 1.2 is a true desk day with almost no walking. 1.375 is light activity or 1–3 training sessions. 1.55 is moderate training or a high step count. 1.725 is daily hard training or a physical job. 1.9 is rare: physical job plus serious sport. Most people overshoot by one full band. If StepDay shows 4,000 steps and three 40-minute lifts, you are not 1.9. Write the product as TDEE, not as “BMR.”
Weigh a few mornings per week and watch the weekly average. If you eat the calculated TDEE and the average climbs, the factor was high or portions drifted. If it falls while you meant to maintain, the factor was low or you are under-eating relative to the log. Adjust ±100 kcal, not a whole activity band, unless steps clearly jumped a category. BMR itself only needs a fresh equation when weight or age inputs change.
Retest the equation after about 5 kg of loss or gain, after a job that changes standing time, after a season that kills or creates a walking commute, and after you add or drop a training block. Do not retest because a social post said “BMR is a myth.” Equations are models; the scale is the audit. If you are ill, pregnant, or have a thyroid or metabolic diagnosis, a clinic measurement and a clinician beat this page.
Formulas, reference tables, and practical guidance you can come back to.
Activity multipliers exist because BMR stops at the bed. The classic Harris-Benedict-style bands — 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active, 1.9 extra active — are still the ones most web calculators paste. They are coarse. Two people with the same gym calendar can differ by thousands of steps. Treat the table as a starting label, then audit with a week of steps and a scale trend. A desk job under about 5,000 steps and no training is 1.2. The same desk plus 1–3 lifts or a 7,500-step habit is 1.375. Training 3–5 days or a solid 10,000-step baseline is 1.55. Daily hard sessions or a physical job is 1.725. 1.9 is physical job plus serious sport — if you are unsure, you are not 1.9. Write the product as TDEE. Quoting “my BMR is 2,400” after multiplying by 1.55 is how forum arguments start.
Overestimating the factor is the most common failure mode, larger than picking Harris-Benedict over Mifflin. People remember the hour they trained and forget the nine hours they sat. If you want a conservative start, choose the lower adjacent band and eat there for 14–21 days. A rising weekly weight average means the true TDEE is lower than the label; a falling average while you meant to maintain means the opposite. StepDay’s step and workout trends are the cheapest way to see which row you actually live in. This table is educational, not a VO2 or occupational-metabolic survey, and not medical advice.
| Label | Factor | Typical week |
|---|---|---|
| Sedentary | 1.2 | Desk, <~5,000 steps, no training |
| Lightly active | 1.375 | 1–3 sessions or ~7,500 steps |
| Moderately active | 1.55 | 3–5 sessions or 10,000+ steps |
| Very active | 1.725 | Daily hard training or physical job |
| Extra active | 1.9 | Physical job plus serious sport |
Mifflin-St Jeor (1990) was derived from a more recent sample than the original Harris-Benedict work and usually wins accuracy contests in healthy adults when the reference is measured resting metabolic rate. Men: 10W + 6.25H − 5A + 5. Women: 10W + 6.25H − 5A − 161. Weight is kilograms, height centimeters, age years. Harris-Benedict 1919 used a smaller, earlier cohort; the 1984 Roza and Shizgal revision updated coefficients but still tends to run slightly high versus modern calorimetry in many groups. Example: a 30-year-old man, 175 cm, 70 kg. Mifflin BMR is about 1,649 kcal. Revised Harris-Benedict for the same inputs typically lands a little higher (often around 1,700+). That gap is coefficients, not “metabolism changing between tabs.”
Neither formula is a medical diagnosis. Both assume you are a typical adult without the extras a cart would see: fever, late pregnancy, high-dose stimulants, very low energy availability, or large deviations in lean mass. Katch-McArdle needs body fat and is not this page. If two apps disagree, check units (lb vs kg, inches vs cm) before you invent a third lifestyle. Prefer Mifflin for a plan, keep Harris in view so you understand the spread, then let the scale and an honest activity factor settle the argument. Educational use only.
| Equation | Men | Women |
|---|---|---|
| Mifflin-St Jeor (1990) | 10W + 6.25H − 5A + 5 | 10W + 6.25H − 5A − 161 |
| Harris-Benedict revised (1984) | 88.362 + 13.397W + 4.799H − 5.677A | 447.593 + 9.247W + 3.098H − 4.330A |
| Worked example (M, 30y, 175 cm, 70 kg) | Mifflin ≈ 1,649 kcal | Then × factor = TDEE |
| Typical spread vs Harris | ~50–150 kcal | Coefficients, not a new metabolism |
BMR equations are snapshots of the inputs you typed. They do not drift because you slept badly; they drift when weight, age, or the sex you entered changes, or when you realize height was typed in inches as centimeters. Recalculate after about 5 kg of loss or gain — the 10×weight term moves 50 kcal per 5 kg on Mifflin, which is small next to a wrong activity factor but worth refreshing. Recalculate the factor, not the equation, when you change standing time at work, lose a walking commute in winter, or add a fourth training day. If three weeks of weekly averages disagree with the plan, move food or factor by a small step before you shop for a new formula.
Clinic exceptions beat the calendar. Pregnancy, thyroid disease, fever, recently diagnosed diabetes treatment, and very low energy availability can move resting burn in ways no website should guess. If a physician wants indirect calorimetry, go. If you are recovering from an eating disorder, do not use a BMR widget to justify a smaller plate. For healthy adults changing body weight on purpose, the loop is: Mifflin BMR → honest factor → TDEE → two to three weeks of scale data → ±100 kcal. StepDay sits on the factor side of that loop by showing whether the week was actually 1.375 or 1.55. Educational only — not medical advice.
| Trigger | Recalculate | Why |
|---|---|---|
| ~5 kg weight change | BMR equation | 10×kg term moves ~50 kcal / 5 kg |
| Job / commute / season | Activity factor only | BMR inputs did not change |
| 3-week scale disagreement | ±100 kcal or one factor step | Audit before shopping formulas |
| Pregnancy, thyroid, eating-disorder care | Clinic, not this page | Equations cannot see those states |
Quick answers about this tool and how to train with it.
BMR is the resting component. TDEE is BMR times an activity factor plus, in richer models, the thermic effect of food. On this page TDEE means BMR × 1.2–1.9. Eating your BMR as if it were a daily target is a crash deficit for anyone who leaves the bed. Eating a 1.9 TDEE while sitting 10 hours is a surplus. Keep the labels honest: quote BMR when you mean rest, quote TDEE when you mean the day you actually live.
Trust Mifflin-St Jeor as the default for healthy adults in a general clinic or coaching context. Harris-Benedict is older and often a bit higher; it is useful as a second opinion, not as a reason to eat an extra sandwich. Neither equation knows lean mass, so very muscular or very lean people can sit outside the typical error band of about ±10%. If you have access to a metabolic cart, use it. If not, pick Mifflin, pick a conservative factor, and let three weeks of scale data win arguments.
They describe the whole day, not the hour in the gym. 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active, 1.9 extra active. A construction worker who never “workouts” can out-burn a desk athlete who trains daily. Step counts are a useful tie-break: under ~5,000 steps usually stays in 1.2–1.375 unless the job is standing-heavy; 10,000+ steps plus training often justifies 1.55. 1.9 is for people who are tired at 8 p.m. because of work plus sport, not because of a single HIIT video.
Retest the equation when weight has moved about 5 kg, when age ticks a birthday that you actually entered, or when a clinician wants a new baseline after illness or medication change. Retest the activity factor far more often — any time the commute, job, or training block changes. You do not need a new BMR because you had a salty dinner or a late night. If the weekly weight average fights the plan for three weeks, change intake or factor first; only reopen the equation if the inputs themselves are stale.
Neither. Predictive equations estimate resting burn from age, sex, height, and weight. They do not measure oxygen consumption. They do not see thyroid disease, fever, pregnancy, amputation, or very high muscle mass. Do not use this page to self-treat unexplained weight change. If a physician ordered a metabolic test, that number overrides both formulas. For everyone else, Mifflin plus an honest factor plus a scale audit is a workable coaching start — and StepDay keeps the factor honest by showing the week you actually walked.
More free tools that pair well with this one, plus guides and articles to go deeper.
Daily calorie needs from the Mifflin-St Jeor formula, with lose, maintain, and gain targets.
Open toolDaily protein from 0.8–2.2 g/kg, with a 70 kg example and meal-split guidance.
Open toolBody mass index with WHO category and the healthy weight range for your height — metric and imperial.
Open toolOne copy-paste gives your readers the full interactive widget — free.
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StepDay turns Apple Health steps, workouts, and sleep into trends so you can see whether 1.375 or 1.55 is actually yours — free on the App Store.