A calorie deficit is the state of eating fewer calories than your body burns in a day. Every fat-loss method — whether it calls itself keto, intermittent fasting, low-carb, or flexible dieting — works through a deficit. The food choices change. The deficit doesn't.
This calorie deficit calculator helps you find the right daily target for your body and goal, using the same Mifflin–St Jeor + activity multiplier math used in our main TDEE calculator. The page also covers how big a deficit to use, how to verify it works, and how to adjust as your weight changes.
How to calculate your deficit in two steps
Calculating a calorie deficit is a two-step process. First find your maintenance calories (TDEE), then subtract the deficit. The exact maintenance number depends on your age, weight, height, gender, and activity level.
Step 1 — Find TDEE
Use the Mifflin–St Jeor equation: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5 (men) or −161 (women). Multiply by 1.2 to 1.9 depending on activity level.
Step 2 — Subtract the deficit
Subtract 300–500 calories per day for moderate fat loss. Larger deficits work faster but increase muscle loss and adherence problems. Never eat below your BMR for long stretches without medical supervision.
How big should your deficit be?
Deficit size determines how fast you lose body fat and how well you keep muscle while doing it. Bigger isn't better — the right size balances speed, sustainability, and lean-mass preservation.
| Deficit | Weekly loss | Best for |
|---|---|---|
| 250 kcal/day | ~0.25 kg | Late-stage cuts; very sustainable. |
| 500 kcal/day | ~0.5 kg | The standard. Balance of speed and adherence. |
| 750 kcal/day | ~0.7 kg | Heavier individuals with body fat to lose. |
| 1,000+ kcal/day | 1+ kg | Short-term only; risk of muscle loss. |
Macros while in a deficit
Protein is the macronutrient that protects muscle while you cut. Aim for 1.8–2.4 g per kg of body weight. Fat at 0.7–1.0 g per kg keeps hormones in check. The rest of your calories come from carbohydrates, which fuel training and recovery.
Why deficits stop working over time
As you lose weight, your TDEE drops — both because you have less mass to move (about 13 kcal per kg of lean mass lost) and because the body adapts metabolically through reduced NEAT and slightly lower BMR. A deficit that worked at week 1 may be near maintenance by week 12.
Recalculate TDEE every 5 kg of weight change or every 8 weeks, whichever comes first. Take a 1-week diet break at maintenance every 8–10 weeks to restore some lost adaptive thermogenesis. See our full guide on what a calorie deficit is for the deeper context.
Calorie deficit examples by body type
Real numbers for typical adults at moderate activity, using a 500-calorie deficit.
- BMR
- 1,762 kcal
- TDEE
- 2,732 kcal
- Fat-loss target
- 2,232 kcal/day
- Protein (2 g/kg)
- 160 g
Expected loss: ~0.5 kg/week. After 12 weeks: ~6 kg lost, recalculate TDEE.
- BMR
- 1,431 kcal
- TDEE
- 2,218 kcal
- Fat-loss target
- 1,718 kcal/day
- Protein (2 g/kg)
- 140 g
If the 7-day rolling weight isn't trending down after 3 weeks, drop 100 kcal.
- BMR
- 1,809 kcal
- TDEE
- 2,171 kcal
- Fat-loss target
- 1,671 kcal/day
- Protein (2.2 g/kg)
- 210 g
Add 4,000+ daily steps to widen the deficit without eating less.
Common mistakes and misconceptions
- Going too aggressive. 1,000+ kcal deficits crash adherence and burn muscle. Cap at 25% below TDEE.
- Ignoring weekend overshoots. Bodies respond to weekly totals. Two heavy weekend days can erase a 5-day deficit.
- Skipping protein. Below 1.2 g/kg, weight loss includes far more muscle than necessary.
- Never recalibrating. A deficit that worked at week 1 needs adjustment by week 8–12.
Tips for a deficit that actually works
- Track weight as a 7-day rolling average. Daily numbers swing 1–2 kg from water.
- Front-load the day with protein and vegetables — calorie targets get easier when the first 700 calories are filling.
- Use a food scale for the first 4 weeks. Eyeballing portions is the most common cause of stalls.
- Build one planned higher-calorie meal per week so restriction feels less permanent.
People also ask
What is the safest calorie deficit?
Can I create a deficit through exercise instead of eating less?
How long should I stay in a calorie deficit?
Why am I not losing weight on a calorie deficit?
Will I lose muscle in a calorie deficit?
Related calculators & guides
- Main TDEE & Body Fat Calculator — all numbers in one screen
- What is a calorie deficit? — deeper explanation
- Calories to lose weight — deficit sizing
- How to reduce body fat — full fat-loss protocol