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TDEE on GLP-1

Total Daily Energy Expenditure is the number of calories your body burns in a day at your current activity level. On a GLP-1, knowing your TDEE is the difference between an effective deficit and accidentally eating below your basal needs.

GLP-1 medications make eating less feel effortless, which is the point — but they also make it remarkably easy to slide into a deficit so deep that you lose muscle, energy, and hair. Knowing your TDEE gives you a hard floor (do not eat below 80% of this number for sustained periods) and a target (eat at TDEE minus 500-750 calories for steady fat loss).

The most validated equation for estimating TDEE in adults — including adults with obesity, which the older Harris-Benedict equation handles poorly — is Mifflin-St Jeor. You calculate Basal Metabolic Rate (BMR) from your age, sex, height, and weight, then multiply by an activity factor to get TDEE.

This page walks through the math, gives you three worked examples, and explains how to apply your TDEE to a GLP-1 deficit without going below the floor.

The formula

BMR via Mifflin-St Jeor uses metric units. For men: 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. For women: the same equation but minus 161 at the end instead of plus 5. To convert: divide pounds by 2.205 for kilograms, multiply inches by 2.54 for centimeters.

Once you have BMR, multiply by the activity multiplier that matches your real-world activity. Sedentary (desk job, little movement): 1.2. Lightly active (walks, 1-3 light workouts a week): 1.375. Moderately active (3-5 workouts a week): 1.55. Very active (6-7 hard workouts a week): 1.725.

Most people on GLP-1 overestimate their activity level by one tier. If your workouts have shrunk or you have been more tired since starting, drop one level. Activity multipliers also count non-exercise movement, which often falls as appetite drops — the body conserves energy when calories get tight.

The Formula

TDEE = BMR × activity multiplier

BMR (men) = 10W + 6.25H − 5A + 5. BMR (women) = 10W + 6.25H − 5A − 161. W in kg, H in cm, A in years.

Worked examples

Person A: 42yo woman, 5'6" (168cm), 200 lb (90.7kg), sedentary

BMR = 10(90.7) + 6.25(168) − 5(42) − 161 = 1586 kcal. TDEE = 1586 × 1.2 = 1903 kcal/day. Fat-loss target: ~1400 kcal. Floor: ~1500 kcal.

Person B: 35yo man, 5'10" (178cm), 230 lb (104.3kg), lightly active

BMR = 10(104.3) + 6.25(178) − 5(35) + 5 = 1986 kcal. TDEE = 1986 × 1.375 = 2731 kcal/day. Fat-loss target: ~2100 kcal. Floor: ~1800 kcal.

Person C: 55yo woman, 5'4" (163cm), 170 lb (77.1kg), moderately active

BMR = 10(77.1) + 6.25(163) − 5(55) − 161 = 1404 kcal. TDEE = 1404 × 1.55 = 2176 kcal/day. Fat-loss target: ~1600 kcal. Floor: ~1300 kcal.

A note on those floors: the conventional minimums of 1500 kcal/day for men and 1200 kcal/day for women come from population-level data. They are not laws — but going under them for more than a few weeks usually means hair shedding, fatigue, and disproportionate lean-mass loss. On a GLP-1, where appetite makes it weirdly easy to eat 900 calories without noticing, the floor exists to keep you from accidentally wrecking your metabolism.

Where the calculator will live

An interactive TDEE calculator — where you enter your stats, get a BMR and TDEE breakdown, and see a fat-loss target with a built-in floor warning — is on the roadmap. Until then, the NIDDK Body Weight Planner gives an academic-grade TDEE estimate and lets you simulate different calorie deficits over time.

Common questions

Common Concerns

Does being on a GLP-1 lower my TDEE?expand_more

Indirectly, yes. As you lose weight, your BMR drops (a smaller body burns less). And as appetite drops, non-exercise activity often falls too — people fidget less, walk less, take fewer trips up the stairs. Recalculate TDEE every 15-20 lb of weight loss to keep your target current.

Should I eat back exercise calories?expand_more

Mostly no. Most fitness trackers overestimate calorie burn by 30-50%. If you used a moderate activity multiplier in your TDEE calculation, your workouts are already baked into the number. Only consider adding back food for unusually long sessions (90+ minutes) or events outside your normal pattern.

What if I cannot even hit my deficit target?expand_more

Many GLP-1 users underconsume relative to their TDEE-minus-500 target, especially in the first few months. That accelerates initial loss but increases muscle-loss risk. Focus on hitting protein and your calorie floor first, deficit second. The drug will handle the rest.

Is Mifflin-St Jeor accurate for higher BMIs?expand_more

More accurate than the older Harris-Benedict, which overestimates BMR in adults with obesity. Mifflin-St Jeor is within about 10% of measured BMR for most adults in the BMI 25-40 range. Above BMI 40 or below 18.5, accuracy drops and you should consider a clinical metabolic test if precision matters.

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