How to Calculate a Calorie Deficit in 3 Steps (With Formulas)
Step 1 — Estimate your BMR (calories burned at rest)
Your BMR (Basal Metabolic Rate) is what your body burns just existing — organs, brain, temperature regulation. The Mifflin-St Jeor equation is the standard everyday formula:
Example — David, 35, 85 kg, 178 cm:
BMR = 10×85 + 6.25×178 − 5×35 + 5 = 850 + 1,112.5 − 175 + 5 = ≈ 1,793 kcal
Step 2 — Convert BMR to TDEE (your real daily burn)
Multiply BMR by the factor matching your typical week — and be honest, overestimating activity is the #1 reason deficits "don't work":
| Lifestyle | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little exercise | × 1.2 |
| Lightly active | Exercise 1–3 days/week | × 1.375 |
| Moderately active | Exercise 3–5 days/week | × 1.55 |
| Very active | Hard exercise 6–7 days/week | × 1.725 |
| Extremely active | Physical job + hard training | × 1.9 |
David trains 3–4 days a week → moderately active:
TDEE = 1,793 × 1.55 = ≈ 2,779 kcal/day — his maintenance.
Step 3 — Subtract your deficit
Take 300–500 kcal off your TDEE (see is 500 safe? for choosing your size):
David picks −500:
Target = 2,779 − 500 = ≈ 2,280 kcal/day → expected loss ≈ 0.5 kg (1 lb)/week.
Safety floor: don't go below ~1,200 kcal/day (women) or ~1,500 kcal/day (men) without medical supervision, even if the math suggests it.
Skip the math — get your numbers instantly
BMR, TDEE, deficit target, weekly loss estimate, and predicted goal date — personalized in 30 seconds, free.
After you calculate: the 3 rules that make it work
- Treat the number as a starting estimate, not gospel. Formulas have a ±10% margin. Your scale trend over 2–4 weeks is the real feedback.
- Track honestly for the first two weeks. Weigh food where possible — "one spoon of peanut butter" is rarely one spoon.
- Recalculate every 4 weeks (or every 4–5 kg lost). Your TDEE drops as your weight drops; a static target slowly stops being a deficit.
Troubleshooting: "I calculated it but I'm not losing weight"
- Portions are bigger than logged — the most common cause by far. Re-measure for one week.
- Activity factor too generous — 2 gym visits/week with a desk job is "light", not "moderate".
- Weekends erase weekdays — average your intake over the full 7 days.
- It's only been a few days — water fluctuations mask fat loss; judge on 2–4 week trends.
- Still stuck after 4 honest weeks? Reduce your target by ~150 kcal or add daily steps, then reassess.
This article is for general education and is not medical advice. Calorie needs vary by individual. Consult a qualified healthcare professional before making significant dietary changes, especially if you are pregnant, breastfeeding, under 18, or have a medical condition or history of disordered eating. See our medical review policy and disclaimer.