Daily Calorie Estimate

What the Mifflin–St Jeor estimate is

This page computes resting energy expenditure with the Mifflin–St Jeor equation — the formula most nutrition researchers regard as the best general-purpose predictor without laboratory work — then scales it with an activity factor to a full-day total. The resting part uses age, height and weight, with the female equation's −161 constant instead of the male +5. The activity choice is yours: 1.2 sedentary, 1.375 light, 1.55 moderate, 1.725 very active, 1.9 extra active. Those five numbers represent typical occupational and exercise patterns, not precise formulas of your week.

Before the number, the honesty constraints: it is a population-level estimate, not your metabolism; individual variation commonly spans ±10% and widens with conditions, medications, breastfeeding/pregnancy and atypical body composition. It is not medical or dietary advice, and it is a poor basis for aggressive deficits; bring it to a professional as a starting datum, not an instruction. What it is genuinely useful for: sizing rough targets, comparing yourself to reference days, and opening a conversation with real numbers instead of guesses.

A worked example, step by step

Problem: male equation, age 38, weight 84 kg, height 178 cm, light activity (1.375).

1. Weight term: 10 × 84 = 840.
2. Height term: 6.25 × 178 = 1,112.5.
3. Age and constant: −5 × 38 = −190, then +5.
4. BMR: 840 + 1,112.5 − 190 + 5 = 1,767.5 kcal at rest.
5. Full day: 1,767.5 × 1.375 = 2,430 kcal (the tool rounds to whole kilocalories).

Read that 2,430 as a maintenance ballpark under that activity label, and note how sensitive the total is to the label rather than the body: the same resting figure over the moderate factor (1.55) jumps to 2,740 kcal/day, entirely on a shifted assumption about movement. Accuracy therefore lies mostly in how honestly you pick the activity.

The same body across activity levels (male 38, 84 kg, 178 cm)

The spread is wide: sedentary and extra active on the same body differ by 1,237 kcal/day — more than most people identify as "snacking". Getting the label right is the greatest error-prevention move available on this page.

From the number to the decision

Single estimates age badly; bodies and routines do not sit still. Treat the 2,430 as a provisional plan: hold it for two to three weeks against real eating and weight-trend data, then recalibrate — every 5 kilograms of body weight moves the resting figure about 50 kcal (the 10 × weight term makes that shift linear), so the same male example at 79 kg reads nearer 2,362 kcal under the same activity label. That linear sensitivity is the honest limit of the arithmetic: appetite, sleep, stress and prescription drugs all sit outside its two coefficients, and together they routinely outdraw the formula's precision.

Keep the activity label honest by re-checking it against a calendar, not an aspiration: the five factors span 2,121 to 3,358 kcal for this one body, a 1,237 kcal band, so an optimistic label invents the equivalent of an entire breakfast. Planned deficits or surpluses belong in a conversation with a doctor or dietitian before acting — the estimate informs the professional decision, it does not replace one — and the hydration side of the same daily routine has its own range to read: the Water Intake Estimator stays a sibling estimate, not a prescription.

Mistakes that disconnect the estimate

• Height/weight in inches or pounds. The formula is metric; convert first or the result is systematically off.
• Action label for intention. Planning to train five days a week is not the same factor as doing it; pick the schedule you keep today.
• Using BMR as diet target. Eating below resting energy for long stretches is a clinical question; this page is not a prescription.
• Women choosing the male constant. The two settings differ by 166 kcal at rest; misplacement then diverts the total by hundreds.
• Same BMR at any age. The −5 × age term moves the baseline materially as years pass; re-estimate rather than carrying an old figure forward.

Keep exploring

• BMI Calculator — the metric-screening status of the same body.
• BMI Calculator (Imperial) — the same BMI with pounds and inches.
• Water Intake Estimator — hydration estimates if activity tracking habits matter.
• Guide: BMI and Calorie Estimates Explained.