How much does BMR drop per year of age?

Under the Mifflin-St Jeor equation, exactly 5 kcal/day per year of age, for a given weight and height, regardless of sex — the formula subtracts 5×age from the weight-and-height component for everyone. Over a decade, that's a 50 kcal/day drop; over 30 years, 150 kcal/day, holding weight and height constant.

Is the age-related drop in BMR really linear?

The formula models it as linear, which is a simplification. Real resting metabolism is affected by muscle mass, hormonal changes, and other factors that don't decline at a perfectly constant rate — but the linear approximation is close enough over adult age ranges to be useful for calorie planning.

Why does BMR fall with age if weight stays the same?

Partly because lean muscle mass tends to decrease with age even at a stable body weight, and muscle burns more calories at rest than fat tissue does. The Mifflin-St Jeor formula doesn't measure muscle mass directly — it captures the age effect as a flat per-year subtraction instead, which approximates the average pattern.

Can I offset the age-related BMR decline?

Maintaining or building muscle mass through resistance training is the most commonly cited approach, since muscle is more metabolically active than fat at rest — but the formula itself doesn't account for training status, so two people the same age, weight, and height get the same BMR estimate regardless of muscle mass. This is general information, not a personalized fitness plan.

Guide

How much does your BMR actually drop as you get older?

Same weight, same height, twenty years apart — the formula alone accounts for a real, measurable drop.

By Buğra SözeriPublished September 25, 2026

Open the Mifflin-St Jeor formula and the age term is easy to miss: − 5 × age. It’s a flat, linear subtraction — every additional year of age knocks exactly 5 calories off the daily BMR estimate, for the same weight and height, whether you’re 25 or 65.

The formula's age term, isolated

Full formula for a 70 kg, 175 cm man:

BMR = 10 × 70 + 6.25 × 175 − 5 × age + 5

Holding weight and height fixed at 70 kg and 175 cm, the weight-and-height component (10×70 + 6.25×175 + 5 = 1,798.75) never changes. Only the −5 × age term moves:

Age	BMR (same 70 kg / 175 cm)
25	1,673.75 kcal/day
35	1,623.75 kcal/day
45	1,573.75 kcal/day
55	1,523.75 kcal/day
65	1,473.75 kcal/day

Forty years of aging, with identical weight and height, costs exactly 200 kcal/day of estimated BMR under this formula — a gradual, steady decline rather than a cliff at any particular age. For women, the same 5×age term applies; only the constant at the end differs (−161 instead of +5).

Why the decline happens

The formula itself doesn’t explain mechanism — it's a statistical fit to measured data, not a physiological model. But the pattern it captures lines up with a well-documented real-world trend: lean muscle mass tends to decrease gradually with age, even when total body weight is stable, and muscle tissue burns more calories at rest than fat tissue does. A 45 kg of muscle at 25 and 45 kg of muscle plus more fat mass at 65 (same total weight) would plausibly burn less at rest — which is the real-world effect the flat per-year subtraction is standing in for.

Because the formula only takes weight, height, age, and sex — not body composition — it can’t distinguish between two 45-year-olds who weigh the same but have very different muscle mass. Both get the identical BMR number. See Mifflin-St Jeor vs. Harris-Benedict for how this formula compares to the older alternative, and what it does and doesn’t account for.

What this means for calorie planning over time

If you're recalculating your BMR periodically — every few years, say — expect the number to drift down slightly even if your weight hasn't changed, purely from the age term. That's expected, not a sign anything is wrong; it's built into the formula, and it's one reason a TDEE target set at 25 shouldn't be assumed to still be accurate at 45 without recalculating. See how to calculate TDEE correctly for the next step after BMR. This is general educational information, not medical or nutrition advice.

Frequently asked questions

How much does BMR drop per year of age?: Under the Mifflin-St Jeor equation, exactly 5 kcal/day per year of age, for a given weight and height, regardless of sex — the formula subtracts 5×age from the weight-and-height component for everyone. Over a decade, that's a 50 kcal/day drop; over 30 years, 150 kcal/day, holding weight and height constant.
Is the age-related drop in BMR really linear?: The formula models it as linear, which is a simplification. Real resting metabolism is affected by muscle mass, hormonal changes, and other factors that don't decline at a perfectly constant rate — but the linear approximation is close enough over adult age ranges to be useful for calorie planning.
Why does BMR fall with age if weight stays the same?: Partly because lean muscle mass tends to decrease with age even at a stable body weight, and muscle burns more calories at rest than fat tissue does. The Mifflin-St Jeor formula doesn't measure muscle mass directly — it captures the age effect as a flat per-year subtraction instead, which approximates the average pattern.
Can I offset the age-related BMR decline?: Maintaining or building muscle mass through resistance training is the most commonly cited approach, since muscle is more metabolically active than fat at rest — but the formula itself doesn't account for training status, so two people the same age, weight, and height get the same BMR estimate regardless of muscle mass. This is general information, not a personalized fitness plan.

Sources & references

Authoritative references cited by this piece. Verified by Buğra Sözeri on the dates shown and re-checked at every deploy.

Mifflin, St Jeor et al., Am J Clin Nutr 1990 — Original derivation of the equation, including the per-year age coefficient used here(as of 2026-09-25)
NIA — Metabolism and Aging (National Institute on Aging) — NIA overview of age-related changes in body composition and energy needs(as of 2026-09-25)