Calorie and macro calculator
Calorie target = Mifflin-St Jeor resting energy × activity factor × goal adjustment. A 30-year-old man, 180 cm and 80 kg, training three times a week to build muscle needs about 2850 kcal a day.
Rest day
2850 kcal
- Protein
- 144 g
- Fat
- 79 g
- Carbs
- 391 g
Training day
3150 kcal
- Protein
- 158 g
- Fat
- 79 g
- Carbs
- 452 g
How it adds up
Resting: 10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 1780 kcal
Target: 1780 × 1.465 × 1.1 = 2868 ≈ 2850 kcal
Training day: 2850 × 1.1 ≈ 3150 kcal
Check your input: age 18–80, height 130–220 cm, weight 40–200 kg, workouts 0–7 per week.
The Mifflin-St Jeor equation
Resting energy expenditure is what your body burns at rest. Mifflin, St Jeor and colleagues published the equation in 1990: 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years), then + 5 for men and − 161 for women.
The result is multiplied by an activity factor based on workouts per week and by a goal adjustment, then rounded to 50 kcal — the formula isn't more precise than that.
Activity factors
| Workouts per week | Factor |
|---|---|
| 0–1 | × 1.375 |
| 2–3 | × 1.465 |
| 4–5 | × 1.55 |
| 6–7 | × 1.725 |
Goal adjustment
| Goal | Calories | Protein, g per kg |
|---|---|---|
| Lose weight | −15 % | 2 |
| Build muscle | +10 % | 1.8 |
| Get stronger | +5 % | 1.8 |
| Endurance | ±0 % | 1.6 |
How protein, fat and carbs are split
Protein is set per kilogram of body weight by goal, fat is a quarter of calories (9 kcal per gram), and carbs are whatever is left (4 kcal per gram).
On a training day calories and protein go up by 10 %, fat stays the same, and the extra goes to carbs — fuel for the workout.
Worked example
Man, 30, 180 cm, 80 kg, 3 workouts a week, goal: muscle. Resting: 10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 1780 kcal. Target: 1780 × 1.465 × 1.1 ≈ 2850 kcal: protein 144 g, fat 79 g, carbs 391 g. On a training day — 3150 kcal.
How accurate is it
The equation describes average people; one person's real burn can differ by hundreds of calories. Treat the target as a starting point: keep it for 2–3 weeks, watch your weight and adjust by 100–200 kcal.
When losing weight, aim for 0.5–1 % of body weight a week: the steeper the deficit, the more of the loss is muscle (review by Helms and colleagues, 2014). If you're losing faster, eat a bit more.
Programs for this goal
Recipes that fit these numbers
Frequently asked questions
How many calories do I need a day?
Work out resting energy with Mifflin-St Jeor and multiply by an activity factor: from 1.375 with no workouts to 1.725 with 6–7 a week. A 30-year-old man, 180 cm and 80 kg, training three times a week needs about 2600 kcal to maintain weight.
How many calories should I cut to lose weight?
The calculator lowers the target by 15 %. Aim to lose 0.5–1 % of body weight a week; if it goes faster, add calories to protect muscle.
Why a separate target for training days?
You burn more on a training day, so calories and protein are 10 % higher. Fat stays the same, and the extra goes to carbs.
Is it suitable for teenagers or pregnancy?
No. The calculator is for adults aged 18–80. For teenagers, during pregnancy or breastfeeding, and with medical conditions, a doctor sets the target.
This is an estimate for healthy adults, not medical advice. With an illness, pregnancy or medication, talk to your doctor.
Sources
- Mifflin MD, St Jeor ST et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr, 1990.
- Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr, 2014.
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