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FitDiary

Calorie deficit calculator for weight loss

See how many calories to eat to lose weight at a steady pace, and when you could reach your goal weight. It’s free, works in kg or lb and needs no sign-up.

Your details

Units
Sex
Height

Add it to see roughly when you could get there.

How active are you?
How fast do you want to lose weight?

Your result

Enter your age, height and weight to see your calorie deficit.

What is a calorie deficit?

A calorie deficit means eating fewer calories than your body uses in a day (your TDEE). Your body makes up the difference from its energy stores, so your weight goes down over time. A deficit of 500 kcal a day, or 3,500 kcal a week, works out at roughly 0.5 kg (1.1 lb) a week.

The bigger the deficit, the faster you lose weight, but the harder it is to keep up. That’s why this calculator gives you three paces to choose from instead of a single number.

How the weight loss calorie calculator works

The calculator works in four steps, the same ones the FitDiary app uses to set a weight loss target:

  1. It estimates your maintenance calories (TDEE) with the Mifflin-St Jeor equation and your activity level. You can see the formula step by step on the TDEE calculator page.
  2. It takes off the deficit for your pace: 250, 500 or 750 kcal a day, for about 0.25, 0.5 or 0.75 kg (0.6, 1.1 or 1.7 lb) a week.
  3. If you add a goal weight, it divides the weight to lose by the weekly loss, rounds down to whole weeks and counts that many weeks from today. The weight loss calculator shows the same date with a week-by-week plan.
  4. It checks the result against two limits: your BMR, and a minimum of 1,200 kcal a day for women and 1,500 for men.

Mifflin-St Jeor comes from a 1990 study of 498 healthy adults, and a 2005 systematic review found it the most reliable of the common equations. The minimum intakes come from Harvard Health Publishing, which advises not going below them unless a health professional is supervising.

The FitDiary app sets your daily target with these same numbers and paces.

How big should your calorie deficit be?

A common starting point is 500 kcal a day. A smaller deficit is easier to live with; a bigger one is faster but leaves less room for meals you enjoy.

PaceDeficit a dayDeficit a weekWeekly loss (approx.)
Relaxed250 kcal1,750 kcal0.25 kg (0.6 lb)
Moderate500 kcal3,500 kcal0.5 kg (1.1 lb)
Intense750 kcal5,250 kcal0.75 kg (1.7 lb)

Two limits the calculator checks

  • Your BMR. This is what your body burns at complete rest. If the target falls below it, the calculator warns you and suggests a slower pace.
  • A minimum intake. Harvard Health Publishing advises that calorie intake shouldn’t fall below 1,200 kcal a day for women or 1,500 for men, except under the supervision of a health professional.

The largest deficit offered here is 750 kcal a day, the fastest pace in the FitDiary app. If you’re thinking of going further, talk to a doctor or dietitian first.

Worked example

Take a 30-year-old woman who is 165 cm (5 ft 5 in) tall, weighs 80 kg (176 lb), does light exercise 1–3 days a week and wants to reach 70 kg (154 lb) at the moderate pace:

  1. BMR = 10 × 80 + 6.25 × 165 − 5 × 30 − 161 = 1,520.25, rounded down to 1,520 kcal a day.
  2. TDEE = 1,520.25 × 1.375 = 2,090.3, rounded down to 2,090 kcal a day. This is her maintenance level.
  3. Target = 2,090 − 500 = 1,590 kcal a day, for about 0.5 kg (1.1 lb) a week.
  4. Weeks to goal = 10 kg ÷ 0.5 kg = 20 weeks, about four and a half months.

At the relaxed pace she would eat 1,840 kcal a day and take about 40 weeks. The intense pace would mean 1,340 kcal, which is below her BMR of 1,520, so the calculator flags it.

Calorie deficit at three TDEE levels

How the same three paces work out for three different people:

PersonTDEERelaxed (−250)Moderate (−500)Intense (−750)
Woman, 30, 160 cm, 55 kg, sedentary1,4861,236*986*736*
Woman, 30, 165 cm, 80 kg, lightly active2,0901,8401,5901,340*
Man, 35, 180 cm, 95 kg, moderately active2,9522,7022,4522,202

* Below that person’s BMR. For a shorter, lighter woman who sits most of the day, even the relaxed pace goes slightly below BMR, and the two faster paces fall under 1,200 kcal. Moving more raises her TDEE and leaves more room to eat.

Why weight loss slows down

The weekly figures above are estimates for the first weeks. As you lose weight, your body needs less energy, so the same calories make a smaller deficit. Modelling by the US National Institutes of Health, published in The Lancet in 2011, found that body weight adjusts slowly to a change in calories: about half of the eventual change takes around a year.

In practice, work out your deficit again after every few kilos. With Mifflin-St Jeor, each kilo you lose lowers your BMR by about 10 kcal a day.

Weight also moves up and down from day to day with water, salt and food in your gut. Look at the trend over a few weeks, not at a single weigh-in.

To test your target, eat to it for 2–3 weeks and write down what you eat, for example in a printable food diary, so you can compare your weight trend with what you actually ate.

This calculator is for healthy adults. If you’re pregnant, breastfeeding, under 18, have a medical condition or have had an eating disorder, talk to a doctor or dietitian before you cut calories.

Stick to your deficit without weighing every meal

Type what you ate in one sentence and see how much of today’s target is left. Log your weight and your target updates to match.

Download on the App StoreGet it on Google Play

See how the FitDiary calorie counter works.

Frequently asked questions

How do I calculate my calorie deficit?

Work out your TDEE, the calories you burn in a day, then take off 250 to 750 kcal. A 500 kcal deficit is the usual starting point and comes to about 0.5 kg (1.1 lb) a week. The calculator above does both steps for you.

Is 1,200 calories a day a good deficit?

It depends on your TDEE, not on the number itself. Harvard Health suggests 1,200 kcal as the lowest intake for women without medical supervision, and 1,500 for men. For many people, eating 1,200 kcal means a bigger deficit than they need.

Is a 1,000-calorie daily deficit healthy?

It’s more than the fastest pace in this calculator, which stops at 750 kcal a day. For many people a deficit that size would take them below their BMR or below the minimum intake. If you want to lose weight that fast, talk to a doctor or dietitian first.

How long will it take to lose 20 pounds?

That’s about 9 kg (20 lb). At 1.1 lb (0.5 kg) a week, it takes about 18 weeks; at 1.7 lb (0.75 kg) a week, about 12 weeks; at the relaxed pace, about 36 weeks. Weight loss usually slows as you go, so treat these as the shortest likely times.

If I burn an extra 200 calories a day, how much weight will I lose in a week?

If you eat the same as before, 200 kcal a day is 1,400 kcal a week. Using the same estimate as the calculator, that’s about 0.2 kg (0.4 lb) a week.

What is the most accurate calorie deficit calculator?

Every calculator gives an estimate. This one uses Mifflin-St Jeor, which a 2005 review found the most reliable of the common equations. To find your real number, eat to the target for 2–3 weeks, log what you eat and weigh yourself regularly, then adjust.

Why am I not losing weight in a calorie deficit?

Often the deficit is smaller than it seems: portions and drinks are easy to underestimate, and exercise is easy to overestimate. Water can also hide fat loss for a week or two. If the trend is flat for 3 weeks or more, recalculate and check what you log.

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