Calorie Deficit Calculator for Weight Loss

Calorie Deficit Calculator

Pick how fast you want to lose weight and get the daily calorie target that matches, with a minimum-intake floor so the plan never goes too low and a protein target to protect muscle while you diet.

By the FitStack team. Last updated October 18, 2026. Formulas and sources are listed on this page.

How the calorie deficit is calculated

First the calculator estimates your maintenance calories (TDEE) with the Mifflin-St Jeor equation, or Katch-McArdle if you enter your body fat, times your activity multiplier.¹ It then sizes the deficit from the pace you choose:

Weekly loss (kg) = body weight × pace % Daily deficit = weekly loss × 7,700 kcal ÷ 7 Target = TDEE − daily deficit, but never below 1,200 kcal (women) or 1,500 kcal (men)

For example, an 80 kg (176 lb) person losing 0.5% a week aims for 0.4 kg a week. 0.4 × 7,700 ÷ 7 = 440 kcal a day below maintenance.

Choosing a pace

Pace	Weekly loss	Best for
Gentle	0.25% of body weight	The last few kilos, or when you want training performance to stay high
Steady	0.5%	Most people. Sustainable, with modest hunger
Faster	0.75%	A shorter, more focused diet with high protein and strength training
Aggressive	1%	Short phases only, mostly for people with more weight to lose

Pacing by percentage of body weight scales the deficit to your size. Losing 0.5 to 1% a week is the range associated with keeping lean mass while dieting.⁵

The minimum-intake floor

The 2013 AHA/ACC/TOS obesity guideline describes 1,200 to 1,500 kcal a day for women and 1,500 to 1,800 kcal a day for men as typical weight-loss intakes.⁴ This calculator never suggests less than the bottom of those ranges. If your pace needs a lower number, it holds the floor and tells you loss will be slower. Diets below this level should be supervised by a clinician.

You'll also see a warning when the target falls below your BMR or the deficit is more than 25% of maintenance. Neither is dangerous for a short period, but both make it harder to eat enough protein, train well and keep going.

Why the 3,500-calorie rule breaks down

The rule that 3,500 calories equals a pound of fat (7,700 kcal per kg) works for the first weeks. Over months it over-promises, because as you lose weight your body needs less energy, so the same intake becomes a smaller deficit.² Kevin Hall's dynamic model at the NIH estimates that each 100 kJ (about 24 kcal) cut from daily intake eventually lowers body weight by about 1 kg, but it takes about a year to get halfway there and roughly three years to reach 95% of the change.³

That is why your target is a starting point. Recalculate every 4 to 5 kg, or let your logs do it. The weight loss timeline calculator shows how much this slowing affects your goal date.

Deficit, protein and training together

Calories decide how much weight you lose; protein and strength training decide how much of it is fat. Aim for about 1.6 to 2.2 g of protein per kg of body weight while dieting and keep lifting two to three times a week. The protein calculator sets your number, and the macro calculator splits the rest of your calories into carbs and fat.

Frequently asked questions

Is a 1,000-calorie deficit safe?

For some people with a lot of weight to lose, a 1,000-calorie daily deficit can be reasonable for a period, but for most it is too steep. It often means eating below the 1,200 (women) or 1,500 (men) calories that guidelines suggest as a minimum without medical supervision, and it raises the share of weight lost from muscle. A deficit that loses 0.5 to 1% of your body weight a week is a better default.

Why am I not losing weight in a calorie deficit?

Usually because the deficit is smaller than it looks. Food logs commonly miss oils, drinks and weekend meals; daily movement drops when you diet; and water retention can hide fat loss for one to two weeks. Weigh yourself daily, compare weekly averages, and if nothing has changed after three weeks of accurate logging, lower intake by 100 to 150 calories.

Should I eat back the calories I burn exercising?

No, not if you chose your activity level honestly. The activity multiplier already includes your usual training. Fitness trackers also tend to overestimate exercise calories. Only add food on unusually long sessions, such as a 2-hour hike that isn't part of your normal week.

How long should I stay in a calorie deficit?

Most people do well with 8 to 16 weeks of dieting, followed by at least a few weeks at maintenance before starting again. Long, unbroken diets get harder to stick with as hunger rises and energy drops. Planned maintenance breaks also give you practice holding your new weight.

Do diet breaks work?

Taking one to two weeks at maintenance calories every 8 to 12 weeks can make a long diet easier to sustain and may help preserve training performance. The evidence that they speed up fat loss is mixed, but they rarely slow it down if you return to the deficit afterwards.