How to calculate TDEE by hand — step by step, with worked examples

Step 1: Calculate BMR using Mifflin-St Jeor

Mifflin-St Jeor is the modern consensus formula for predicting basal metabolic rate. It has separate constants for biological females and males, but otherwise the inputs are the same: weight in kilograms, height in centimeters, age in years.

For males: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5

For females: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

The constants (−161 for females, +5 for males) account for the average difference in lean body mass between sexes. If you've come across the older Harris-Benedict formula, you'll notice Mifflin-St Jeor is simpler — and that simplicity isn't a downgrade. Frankenfield's 2005 comparison of predictive equations found Mifflin-St Jeor was the most accurate across a wide range of body sizes, slightly outperforming Harris-Benedict even in its revised 1984 form.

Step 2: Multiply by your activity factor to get TDEE

Once BMR is calculated, multiply it by the activity factor that best matches your real lifestyle. Honest selection matters — most people overstate.

Sedentary (×1.2): desk job, almost no exercise, fewer than ~5,000 steps per day. This is more common than people admit.

Lightly active (×1.375): desk job + 1–3 sessions of exercise per week, OR a moderately active life (8,000–10,000 daily steps) with no formal training.

Moderately active (×1.55): desk job + 3–5 sessions of solid exercise per week, OR a job that keeps you on your feet (server, retail, nursing) + light exercise.

Very active (×1.725): hard training 6–7 days per week, OR a physical job (construction, manual labor) + regular gym work.

Extra active (×1.9): physical job AND daily intense training. Rare. Most people overestimate themselves into this tier — only place yourself here if you genuinely cannot eat without losing weight.

Worked example A: 28-year-old woman, 5'5" (165 cm), 145 lb (65.8 kg), lightly active

Step 1 — BMR (Mifflin-St Jeor, female): BMR = (10 × 65.8) + (6.25 × 165) − (5 × 28) − 161 BMR = 658 + 1,031.25 − 140 − 161 BMR ≈ 1,388 kcal/day

Step 2 — Apply activity factor (Lightly active = 1.375): TDEE = 1,388 × 1.375 ≈ 1,909 kcal/day

Step 3 — Goal-adjust. For a moderate cut (20% below TDEE): Target = 1,909 × 0.8 ≈ 1,527 kcal/day Deficit = 1,909 − 1,527 = 382 kcal/day, or roughly 0.75 lb/week.

Protein anchor at 2.0 g per kg of body weight: 65.8 × 2.0 ≈ 132 g of protein. Fat at 25% of total calories: 1,527 × 0.25 ÷ 9 ≈ 42 g of fat. Carbs fill the rest: (1,527 − (132 × 4) − (42 × 9)) ÷ 4 ≈ 156 g of carbs.

Worked example B: 42-year-old man, 6'0" (183 cm), 195 lb (88.5 kg), moderately active

Step 1 — BMR (Mifflin-St Jeor, male): BMR = (10 × 88.5) + (6.25 × 183) − (5 × 42) + 5 BMR = 885 + 1,143.75 − 210 + 5 BMR ≈ 1,824 kcal/day

Step 2 — Apply activity factor (Moderately active = 1.55): TDEE = 1,824 × 1.55 ≈ 2,827 kcal/day

Step 3 — Goal-adjust. For a lean bulk (10% above TDEE): Target = 2,827 × 1.10 ≈ 3,110 kcal/day Surplus = 3,110 − 2,827 = 283 kcal/day, or roughly +0.5 lb/week — about half muscle, half fat for an intermediate lifter.

Protein anchor at 2.0 g per kg: 88.5 × 2.0 ≈ 177 g of protein. Fat at 25% of total calories: 3,110 × 0.25 ÷ 9 ≈ 86 g of fat. Carbs fill the rest: (3,110 − (177 × 4) − (86 × 9)) ÷ 4 ≈ 408 g of carbs.

If you'd rather use Katch-McArdle (requires body fat %)

Katch-McArdle is often more accurate for lean or muscular bodies, because it calculates BMR from lean body mass rather than total weight. To use it, you need a reliable body fat percentage (DEXA, BodPod, or carefully-taken calipers; don't trust bioelectrical impedance scales).

1. Compute lean body mass: LBM = weight × (1 − body fat % / 100). Example: 180 lb × (1 − 0.18) = 147.6 lb of LBM. Convert to kg: 147.6 × 0.4536 ≈ 67 kg.
2. Apply Katch-McArdle: BMR = 370 + (21.6 × LBM in kg). Example: 370 + (21.6 × 67) ≈ 1,817 kcal.
3. Multiply by your activity factor as in Step 2 above.

Katch ignores age and sex entirely. That's a strength if your lean mass is unusual for your demographic, and a weakness if your body fat estimate is unreliable.

Common arithmetic mistakes to watch for

If your manually-calculated BMR doesn't match the calculator on this site to within a couple of calories, the issue is almost always one of three things.

First — you used inches and pounds without converting to cm and kg. Mifflin-St Jeor doesn't have an imperial form; you must convert.

Second — you used the wrong constant. Female ends with −161, male ends with +5. People sometimes flip them or forget the constant entirely.

Third — you used age in months or in 'years and months' form. The formula wants whole years.

If you've got a calculator handy and you're still off, double-check that you typed 6.25 (not 6.5 or 6) for the height coefficient. That one trips people up.

What to do after you've got your number

Calculation is the easy part. The harder part is verification, which is the only thing that gets you to your true TDEE. Eat at your calculated number for 2 weeks, weigh in daily under the same conditions, and average days 1–7 vs. days 8–14. The trend between those averages is your real signal. If your weight is trending the wrong direction or the wrong speed for your goal, adjust by 100 kcal and re-test for another 2 weeks. After three of these cycles, you'll know your real TDEE to within ~50 kcal — closer than any formula can ever give you.

A fully worked example, start to finish

Let's walk all the way through for a hypothetical person: a 34-year-old woman, 5'6" (168 cm), 155 lb (70.3 kg), who lifts 3× weekly and walks her dog 30 minutes a day.

Step 1 — BMR using Mifflin-St Jeor (female): (10 × 70.3) + (6.25 × 168) − (5 × 34) − 161 = 703 + 1,050 − 170 − 161 = 1,422 kcal/day.

Step 2 — pick the activity multiplier. Three lifting sessions per week plus a 30-min daily walk puts her in 'lightly active' (1.375) if she's otherwise sedentary, or 'moderately active' (1.55) if she has a non-desk job. Assume desk job → 1.375.

Step 3 — TDEE: 1,422 × 1.375 = 1,955 kcal/day.

Step 4 — pick a goal. If she wants to lose fat at a moderate pace: 20% deficit = 1,955 × 0.80 = 1,564 kcal/day. If she wants to maintain: 1,955. If she wants to lean-bulk: 1,955 × 1.08 = 2,111 kcal/day.

Step 5 — protein anchor. At 70.3 kg, a cut target of 2.0 g/kg = 141 g protein/day. Maintenance can be lower (1.6 g/kg = 113 g).

Step 6 — verify. She eats at 1,564 kcal/day for two weeks, weighs daily under consistent conditions, averages week 1 (155.4 lb) and week 2 (154.5 lb). 0.9 lb/week down — matches the moderate-cut expectation. Calculator was accurate; she keeps going.

If instead week 1 average was 155.4 and week 2 average was 155.5 (flat), her real TDEE is lower than the formula predicted — drop target by 100 kcal (to 1,464) and re-verify. After 1–2 such corrections, she'll have her real number.