The question "how many calories should I eat?" sounds simple. The answer requires five inputs, one equation, one multiplier, one goal adjustment, and a floor you should never go below. Here is the full walkthrough — no calculator required, though we will give you one at the end.
Step 1: Calculate your BMR (basal metabolic rate)
Your BMR is the number of calories your body burns at complete rest — running your organs, maintaining body temperature, replacing cells. It accounts for roughly 60–70% of your total daily burn and is the foundation of every calorie target.
The most validated formula for estimating BMR in non-clinical populations is the Mifflin–St Jeor equation, published in 1990 and still the one most registered dietitians use:
Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5 Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161 Non-binary/prefer not to say: use the average, or use the female formula as a conservative estimate.
Example: a 34-year-old woman, 163 cm, 74 kg: (10 × 74) + (6.25 × 163) − (5 × 34) − 161 = 740 + 1018.75 − 170 − 161 = 1,427 kcal/day at rest.
Step 2: Apply your activity factor (this is where people go wrong)
BMR only tells you what you burn lying completely still. To find your total daily energy expenditure (TDEE), you multiply BMR by an activity factor. Most people overestimate this by one tier, which is why many calorie targets end up too high.
| Activity Level | Definition | Multiplier |
|---|---|---|
| Sedentary | Desk job, no structured exercise | × 1.30 |
| Lightly active | 1–2 workouts/week or light walking daily | × 1.45 |
| Moderately active | 3–4 workouts/week, active job | × 1.60 |
| Very active | 5+ hard workouts/week or physical job | × 1.80 |
People who exercise 3×/week tend to pick "moderately active" and add their workout calories on top. Pick your tier based on your real week — including sedentary hours at a desk. If in doubt, pick the lower tier.
Step 3: Adjust for your goal
Your TDEE is your maintenance level — the number of calories at which your weight stays roughly stable. To change your weight or composition, you add or subtract a goal adjustment:
| Goal | Adjustment | Expected rate of change |
|---|---|---|
| Lose body fat | −500 kcal/day | ~0.5 kg/week (1 lb) |
| Aggressive fat loss | −750 kcal/day | ~0.75 kg/week |
| Build muscle (lean) | +250–300 kcal/day | 0.25–0.5 kg/month |
| Improve health / maintain | 0 | No weight change targeted |
A −500 kcal deficit is the most replicated, sustainable rate in the clinical literature. Larger deficits accelerate muscle loss and metabolic adaptation — the point at which your body slows its burn rate to compensate for under-eating.
Step 4: Apply the floor
Your final target should never go below 1,400 kcal/day for women or 1,600 kcal/day for men, regardless of how the math comes out. Below these thresholds, protein needs cannot be met from food alone, nutrient deficiencies compound quickly, and metabolic adaptation kicks in within weeks, making fat loss progressively harder.
The full calculation — a worked example
Using the same 34-year-old woman from step 1 (BMR: 1,427 kcal), lightly active (× 1.45), goal of fat loss:
- TDEE = 1,427 × 1.45 = 2,069 kcal
- Goal adjustment = −500 kcal
- Daily target = 1,569 kcal
- Round to nearest 50: 1,550 kcal
- Check floor: 1,550 > 1,400 ✓
- Practical range: 1,400–1,700 kcal (±150)
Why a range beats a single number
The Mifflin–St Jeor equation has a ±10% error margin in healthy adults — meaning the 1,569 kcal result above could legitimately be anywhere from 1,412 to 1,726 kcal. Treating any single number as precise is a statistical error. A range of ±150 kcal around your target accommodates measurement uncertainty, day-to-day variation in activity, and the normal social variability of eating — without sacrificing progress.
What actually matters more than hitting the exact number
- Protein floor (0.7–1g per lb of bodyweight): this is what preserves muscle in a deficit and drives satiety
- Fiber target (25–35g/day): controls hunger better than most interventions
- Meal timing: not magic, but eating on a loose schedule reduces decision fatigue and late-night eating
- Sleep (≥7h): under-sleep raises ghrelin by 24%, making your calorie target significantly harder to hit
Your daily calorie target = TDEE − goal adjustment, but never below your floor. Work with a range (±150 kcal), not a single sacred number. Get your protein first. The rest largely takes care of itself.