How this calculator works
The math is straightforward, the right inputs matter more than the formula. Two steps:
Step 1: BMR from Mifflin-St Jeor
BMR (Basal Metabolic Rate) is what your body burns just keeping you alive — heart beating, organs running, body temperature held — with zero activity on top. The Mifflin-St Jeor equation is the most widely-used estimator and the one most modern fitness apps use:
| Sex | Formula |
|---|---|
| Male | BMR = 10 × kg + 6.25 × cm − 5 × age + 5 |
| Female | BMR = 10 × kg + 6.25 × cm − 5 × age − 161 |
Mifflin-St Jeor was published in 1990 (Mifflin et al., AJCN) and validated against indirect calorimetry across thousands of subjects. It's accurate to about ±10% for most people. The Harris-Benedict equation (an older alternative) tends to overestimate by ~5%; the Katch-McArdle equation requires a body-fat measurement most people don't have.
Step 2: TDEE from activity factor
BMR alone isn't your maintenance calories — you also burn calories moving, training, and just existing in a daytime state. Multiply BMR by an activity factor:
| Activity level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Desk job, no formal training |
| Light | 1.375 | 1-2 training sessions/week, mostly seated otherwise |
| Moderate | 1.55 | 3-4 training sessions/week (most lifters) |
| Active | 1.725 | 5-6 training sessions/week + reasonably active job |
| Very active | 1.9 | 6+ sessions/week + physically demanding job |
The activity factor is where most calculators go wrong — people tend to overestimate their activity level by one tier. If you have a desk job and lift 4x/week, you're "Moderate" (1.55), not "Active" (1.725).
What the goal target means
The calculator adjusts your TDEE based on the goal you selected:
- Cut: TDEE × 0.8 (20% deficit). Targets 0.5-1% bodyweight loss per week. See the structured cut guide for context.
- Recomp: TDEE × 0.95 (5% deficit). Targets simultaneous fat loss + muscle gain. See the body recomposition guide.
- Lean bulk: TDEE × 1.10 (10% surplus). Targets 0.25-0.5% bodyweight gain per week. See the lean bulk guide.
How macros are calculated
The macro split is goal-adjusted but follows the same priority order: protein first, fat floor, carbs fill in the rest.
| Macro | Cut | Recomp | Lean bulk |
|---|---|---|---|
| Protein | 2.2g per kg | 2.0g per kg | 1.8g per kg |
| Fat | 0.7g per kg (floor) | 0.8g per kg | 0.9g per kg |
| Carbs | Remaining calories | Remaining calories | Remaining calories |
Carbs fill in the calorie budget after protein and fat are set. The result: protein stays high enough to protect lean mass, fat stays above the hormonal floor, carbs fuel training.
How to use these numbers
- Eat at the target for 2-3 weeks. Don't change anything else. Just stick to the calorie and macro targets.
- Track 7-day trend weight, not the daily scale. The trend is the only reliable signal.
- Compare to expected rate. Cut: should lose 0.5-1% of bodyweight per week. Recomp: should be ~flat or slightly down. Bulk: should gain 0.25-0.5% per week.
- Adjust if needed. If you're losing too fast, add 100-200 kcal/day. Too slow, subtract 100-200 kcal/day. Adjust once per 2-week window — not every day.
- Recalculate every 6-8 weeks or after every 5kg of weight change. BMR drops as you lose weight and rises as you gain it.
Why this is a starting point, not a final answer
Three sources of variance the calculator can't account for:
- Your real activity level. The 5-bucket activity factor system is coarse. Real TDEE varies based on NEAT (non-exercise activity thermogenesis), which can swing 200-500 kcal/day between people of identical weight.
- Day-to-day variance in training intensity. A heavy squat day genuinely burns more than a rest day. Static TDEE averages over the week — your daily energy needs don't.
- Adaptation over time. The body downregulates metabolism during cuts and upregulates during bulks. A "true TDEE" today might be 200 kcal off in 6 weeks.
This is why apps that adjust calorie targets based on actual logged data outperform static targets over time. Coachly does exactly that — see the calorie cycling guide for how to handle the day-to-day swings.