What is a calorie deficit?

A calorie deficit is when you eat fewer calories than your body burns in a day (your TDEE). The shortfall forces your body to draw on stored energy — mostly fat — which is what drives weight loss. Eat below your TDEE and, over time, you lose weight.

How big a deficit do I need to lose 1 lb a week?

About 500 kcal a day. One pound of fat stores roughly 3,500 kcal, so a 3,500-kcal weekly shortfall — 500 a day — equals about a pound a week. To lose half a pound, aim for ~250 kcal a day; for a kilogram a week, around 1,100 a day.

Is the 3,500-calorie rule accurate?

It's a useful rule of thumb, not a precise law. Real weight loss slows as you get lighter, water and glycogen shifts blur the early weeks, and metabolism adapts to eating less. Use the 3,500-kcal rule to set a starting target, then adjust based on your actual trend.

What's the smallest safe calorie intake?

As a general guide, intakes below about 1,500 kcal a day for men and 1,200 for women are hard to meet your nutrient needs on and are best done only under professional supervision. If your target falls below that floor, choose a slower rate of loss instead.

Why has my weight loss stalled?

Stalls are normal. As you lose weight your TDEE drops, so a deficit that once worked becomes maintenance; water retention, inconsistent tracking, and metabolic adaptation also play a part. Recalculate your TDEE at your new weight and tighten or recheck your intake.

Calorie Deficit Calculator

This calorie deficit calculator works out the daily deficit and target intake you need to hit your chosen weight-loss rate. It estimates your TDEE, then subtracts the deficit from the 3,500-kcal rule — enter your details in metric or imperial for an instant target.

How it works

A calorie deficit is the gap between what you burn and what you eat. We start from your total daily energy expenditure (TDEE) — your BMR (Mifflin–St Jeor) scaled by an activity factor — then size the deficit from your target rate of loss using the rule that 1 lb of fat ≈ 3,500 kcal(1 kg ≈ 7,700 kcal):

Daily deficit = weekly rate × 3,500 ÷ 7

Target intake = TDEE − daily deficit

(use 7,700 instead of 3,500 when the rate is in kilograms).

Worked example

Say your TDEE is 2,500 kcal and you want to lose 1 lb a week. The daily deficit = 1 × 3,500 ÷ 7 = 500 kcal. So your target intake = 2,500 − 500 ≈ 2,000 kcal a day. Hold that consistently and you should lose roughly a pound a week.

Deficit by weekly rate

How a weekly rate translates into a daily deficit and an approximate monthly loss (rate × 4 weeks):

Weekly rate	Daily deficit	Approx. monthly loss
0.25 lb (0.11 kg)	125 kcal	1 lb (0.45 kg)
0.5 lb (0.23 kg)	250 kcal	2 lb (0.9 kg)
1 lb (0.45 kg)	500 kcal	4 lb (1.8 kg)
1.5 lb (0.68 kg)	750 kcal	6 lb (2.7 kg)

Faster isn't always better — losing more than about 1% of bodyweight per week risks muscle loss. A 0.5–1 lb (0.25–0.5 kg) weekly rate suits most people.

Using your target

Eat at your target intake to lose; eat at your maintenance calories to hold steady. If you'd rather start from the burn side, the TDEE Calculator shows the number this tool subtracts from, and the Macro Calculator splits your target into protein, carbs, and fat.

Frequently asked questions

What is a calorie deficit?: A calorie deficit is when you eat fewer calories than your body burns in a day (your TDEE). The shortfall forces your body to draw on stored energy — mostly fat — which is what drives weight loss. Eat below your TDEE and, over time, you lose weight.
How big a deficit do I need to lose 1 lb a week?: About 500 kcal a day. One pound of fat stores roughly 3,500 kcal, so a 3,500-kcal weekly shortfall — 500 a day — equals about a pound a week. To lose half a pound, aim for ~250 kcal a day; for a kilogram a week, around 1,100 a day.
Is the 3,500-calorie rule accurate?: It's a useful rule of thumb, not a precise law. Real weight loss slows as you get lighter, water and glycogen shifts blur the early weeks, and metabolism adapts to eating less. Use the 3,500-kcal rule to set a starting target, then adjust based on your actual trend.
What's the smallest safe calorie intake?: As a general guide, intakes below about 1,500 kcal a day for men and 1,200 for women are hard to meet your nutrient needs on and are best done only under professional supervision. If your target falls below that floor, choose a slower rate of loss instead.
Why has my weight loss stalled?: Stalls are normal. As you lose weight your TDEE drops, so a deficit that once worked becomes maintenance; water retention, inconsistent tracking, and metabolic adaptation also play a part. Recalculate your TDEE at your new weight and tighten or recheck your intake.

Related calculators

Disclaimer. This is an estimate for general fitness use, not medical or nutritional advice. Extreme deficits are unsafe — if your target falls below the safe floor, slow your rate or consult a qualified professional.