BMR calculator

This tool computes BMR three ways so you can compare:

• Mifflin-St Jeor (1990) — the modern default. The American Dietetic Association's 2005 systematic review found it the most accurate predictive equation for the non-obese and obese adult population. Use this number unless you have a reason not to.
• Harris-Benedict (revised 1984) — the older default, still common in fitness apps. Tends to over-estimate BMR by 5–15%, especially in obese subjects.
• Katch-McArdle (1996) — needs body-fat % as an extra input. Most accurate when you know your body composition (DEXA, BodPod, calipers) because it works off lean body mass directly.

BMR alone isn't your maintenance calorie target — you also burn energy moving. Multiply BMR by an activity factor (PAL):

• 1.2 — Sedentary. Desk job, little or no exercise.
• 1.375 — Light. Light exercise 1–3 days/week.
• 1.55 — Moderate. Moderate exercise 3–5 days/week.
• 1.725 — Active. Hard exercise 6–7 days/week.
• 1.9 — Very active. Hard daily exercise + physical job, or two-a-day training.

The activity factors come from research on physical-activity level (PAL) summarised in the FAO/WHO/UNU 2001 expert consultation. Most people pick a tier too high — if you have a desk job and lift three times a week, "light" or "moderate" is realistic, not "active".

Predictive BMR equations carry a standard error of roughly 8–10% — your true value could be ±150–200 kcal off the displayed estimate. The equations were validated on free-living adults and are less accurate for:

• Children and adolescents — use Schofield or WHO/FAO/UNU equations instead.
• Pregnancy and lactation — energy needs rise materially; consult dietary references for pregnancy.
• Athletes and very lean individuals — Katch-McArdle is the safer bet here.
• Severe obesity (BMI ≥ 40) — Mifflin-St Jeor still wins on average, but personal variation is high.
• Thyroid or metabolic conditions — actual BMR can shift 20%+ from predicted; talk to a clinician.

To maintain weight, eat at TDEE. To lose ~0.5 kg / 1 lb per week, eat at TDEE − 500 kcal. To gain ~0.25 kg / 0.5 lb per week, eat at TDEE + 250 kcal. Aggressive deficits (>25% below TDEE) accelerate fat loss but also accelerate lean-mass loss and metabolic adaptation — sustainable rates are 0.5–1% of body weight per week.

The accompanying calorie calculator wraps the same BMR math with built-in goal offsets and recommended macro splits.