Calorie Deficit Calculator
Find the daily calorie target that produces steady, sustainable weight loss. Enter your sex, age, weight (lb or kg), height (inches or cm), and activity level, then pick a deficit from mild (250 kcal/day) to maximum (1,000 kcal/day).
Example: with Sex Female · Age 35 · Weight 170 · Weight unit lb (pounds) · Height 65 → Daily calorie target: 1,517 kcal/day.
- Maintenance calories (TDEE)2,017 kcal/day
- BMR (Mifflin-St Jeor)1,467 kcal/day
- Projected loss rate≈ 1.0 lb (0.45 kg) per week
Computed by the calculator below using its default values. Change any input to see your own numbers.
BMR from the Mifflin-St Jeor equation; maintenance = BMR × activity multiplier; target = maintenance − your chosen deficit. 3,500 kcal ≈ 1 lb of fat.
How a calorie deficit actually works
Your body spends energy all day: the baseline cost of staying alive (BMR), digesting food, and moving around. Add those up and you get maintenance calories, or TDEE. Eat below that number consistently and your body makes up the difference from stored fat. This calculator estimates BMR with the Mifflin-St Jeor equation — the one a 2005 American Dietetic Association review found most accurate for healthy adults — then multiplies by an activity factor and subtracts your chosen deficit.
The familiar rule that 3,500 kcal equals one pound of fat is a useful planning convention, not a law. As you lose weight, your maintenance number drifts down and your body economizes, so real-world loss runs a bit slower than the math after the first month or two. Re-run the calculator every 10-15 lb.
Picking the right deficit size
Bigger is not better. A 500-750 kcal/day deficit loses fat meaningfully faster than 250 while staying livable; 1,000 kcal/day is hard to sustain, harder to fuel workouts through, and costs more muscle. Keep protein high and lift something a few times a week so the weight you lose is mostly fat. If your target lands below about 1,200 kcal/day, that is a signal to slow down or get professional supervision, not to push through.
How it’s calculated
BMR (Mifflin-St Jeor): men 10×kg + 6.25×cm − 5×age + 5; women 10×kg + 6.25×cm − 5×age − 161. Maintenance (TDEE) = BMR × activity multiplier (1.2 sedentary, 1.375 light, 1.55 moderate, 1.725 very, 1.9 extra). Target = TDEE − deficit. Weekly loss uses the 3,500 kcal ≈ 1 lb (0.454 kg) convention. Conversions: 1 lb = 0.45359237 kg; 1 in = 2.54 cm.
Individual metabolism varies around these population equations by roughly ±10%, and loss slows as your body adapts — treat this as an educational estimate, not medical advice; see a clinician or registered dietitian before a large or extended deficit.
What each deficit size delivers
| Deficit | Per week | Per month | Best for |
|---|---|---|---|
| 250 kcal/day | ≈ 0.5 lb | ≈ 2.2 lb | Last few pounds; minimal hunger |
| 500 kcal/day | ≈ 1.0 lb | ≈ 4.3 lb | The standard sustainable cut |
| 750 kcal/day | ≈ 1.5 lb | ≈ 6.5 lb | Shorter, disciplined cuts |
| 1,000 kcal/day | ≈ 2.0 lb | ≈ 8.7 lb | Higher starting weights, ideally supervised |
Computed with 3,500 kcal ≈ 1 lb of fat; months use 4.35 weeks. Actual loss runs slower over time as maintenance falls.
Common mistakes
- Never recalculating — as you get lighter your TDEE drops, so a fixed intake quietly becomes a smaller deficit.
- Counting exercise twice: choosing an active multiplier and then also eating back the workout calories your tracker reports.
- Cutting below 1,200 kcal/day (women) or 1,500 (men) without medical supervision because the math said so.
- Judging by single weigh-ins — 1-3 lb of water swing hides a real deficit; trust weekly averages.
Frequently asked questions
How is my calorie deficit target calculated?
BMR from Mifflin-St Jeor (men: 10×kg + 6.25×cm − 5×age + 5; women: same minus 166 more), times an activity multiplier for maintenance, minus your chosen deficit. Example: a 35-year-old, 170 lb, 5 ft 5 in lightly active woman maintains on about 2,017 kcal, so a 500 kcal deficit puts her target near 1,517 kcal/day.
How many calories should I cut to lose 1 lb a week?
About 500 kcal/day, using the 3,500 kcal-per-pound convention. Expect the true pace to ease off after a few weeks as your body adapts and your maintenance number falls with your weight.
Why am I not losing weight in a deficit?
Usually the deficit is smaller than it looks: untracked bites and oils, an optimistic activity multiplier, or water retention masking fat loss. Track honestly for 3-4 weeks and compare weekly averages before concluding the math failed.
Is a 1,000-calorie deficit safe?
Only really appropriate for people with a lot of weight to lose, and best done under medical supervision. For lighter people it tends to burn muscle, tank energy, and rebound. If you have any medical condition or a history of disordered eating, involve a doctor or dietitian first.
Should I eat back exercise calories?
Not if your activity multiplier already includes your workouts — that would count them twice. Eat back a portion only if you chose sedentary and then did unusual extra training.