A calorie deficit takes three numbers to find. What you burn in a day, the pace you want, and the gap between them. This guide works out all three with your own answers, then shows how long the gap takes to reach your goal.
What is a calorie deficit?
A calorie deficit means you eat less energy than you burn. Your body makes up the difference from what it has stored, and your weight goes down over time.
In this example, the formula puts your burn at about 2,783 kcal a day. Eat 2,284, and you eat 499 kcal less than that. That gap is your deficit.
What you burn in a day is your TDEE, or total daily energy expenditure. It is also called your maintenance calories. Eat that much, and your weight stays about the same. Eat less, and you are in a deficit. The TDEE calculator explains each part of that number.
How to calculate your calorie deficit by hand
Step 1: Find your TDEE
Start with your resting burn. The Mifflin–St Jeor equation uses your weight in kilograms, your height in centimeters, and your age1. Then multiply the result by your activity level. In this example, the resting burn is 1,795 kcal, and 1,795 × 1.55 = 2,783 kcal a day.
Step 2: Turn your pace into calories a day
A common rule of thumb says a pound of body weight holds about 3,500 kcal (about 7,700 kcal a kilogram)3. Multiply your weekly pace by 3,500, then divide by 7 days. One pound a week is about 500 kcal a day.
Step 3: Take it off your TDEE
In this example, 1 lb a week is 1 × 3,500 ÷ 7 = 499 kcal a day. Your TDEE is 2,783, so you eat 2,783 − 499 = 2,284 kcal a day.
The Fit Shapes app does the same math with the kilogram figure, so its answer can differ from the rounded rule by a calorie or two.
How big should your calorie deficit be?
Your deficit sets your pace. A bigger gap loses weight faster, and it is a bigger gap to live with every day.
| Pace | Daily deficit | Your target |
|---|---|---|
| Lose 0.5 lb (0.23 kg) a week | 250 | 2,533 |
| Lose 1 lb (0.45 kg) a week | 499 | 2,284 |
| Lose 1.5 lb (0.68 kg) a week | 748 | 2,034 |
| Lose 2 lb (0.91 kg) a week | 998 | 1,785 |
A 500 calorie deficit is about 1 lb (0.45 kg) a week. In this example, that is a target of 2,283 kcal a day. A 1,000 calorie deficit is about 2 lb (0.9 kg) a week, a target of 1,783.
Fit Shapes suggests 0.5 to 1.5 lb (0.25 to 0.7 kg) a week. A slower pace takes longer, but it is easier to keep up, and it leaves more room for the foods you like. The CDC says people who lose about 1 to 2 lb a week are more likely to keep the weight off than people who lose it faster4.
If you lift and want to keep your muscle, aim lower. A review for natural bodybuilders sets the pace at about 0.5 to 1% of body weight a week5. In this example, 1% of 185 lb is about 1.9 lb a week, the top of that range.
Fit Shapes never sets a target under 1,200 kcal a day, or under 60% of your TDEE. In this example, that minimum is 1,670 kcal. When a pace goes under it, the target stops at the minimum, and you lose more slowly. The rings at the top show it as a yellow mark.
How long will it take to reach your goal weight?
Divide the weight you want to lose by your weekly pace. To lose 20 lb (9 kg) at 1 lb (0.45 kg) a week takes about 20 weeks.
Type a goal weight in the sentence at the top, and this line shows when you’d reach it at your pace.
That date is a straight line, and the real line bends. A smaller body burns less. Each 10 lb (4.5 kg) you lose takes about 70 kcal a day off your TDEE at your activity level. So the same target makes a smaller gap as the weeks go on, and the last pounds come off more slowly than the first. The TDEE guide shows the formula behind it.
Researchers have measured how far off the straight line is. A 2011 model in The Lancet found that the 3,500 kcal rule leads to much higher expectations than people reach, because it ignores how the burn changes as weight changes2. In that model of an adult with overweight, each change of 10 kcal a day moves your weight by about 1 lb in the end, but it takes about a year to get halfway there2. A 2013 commentary reached the same verdict on the rule3.
So this page calls the date an optimistic estimate. It is the earliest day the math allows. Your scale will also jump from day to day with water, salt, and food, so judge your pace on the trend over a few weeks.
How many calories to eat to lose weight
Eat your TDEE minus your daily deficit.
In this example, to lose 1 lb a week, eat 2,284 kcal a day. That is 499 under the 2,783 you burn.
The minimum above is a floor, not a target to aim for. For a small body, that minimum can be more than you burn, and the calculator then sets no deficit at all. In that case, or if you are under 18, pregnant, breastfeeding, or have a medical condition, ask a doctor or a registered dietitian for a target. This calculator gives an estimate, not medical advice.
How to eat in a calorie deficit
The number is the easy part. The days are harder. Three habits do most of the work.
Eat enough protein. Protein helps you keep muscle while you lose fat. A review for lifters in a deficit suggests 2.3 to 3.1 g per kilogram of lean mass a day5. The protein calculator finds your number from your weight and your goal.
Fill up on foods with more water. Foods with fewer calories for their weight, such as fruit, vegetables, and soups, help you feel full and eat less at a meal7. People tend to eat about the same weight of food, so a lighter plate in calories still looks like a meal.
Log what you eat. A review found 15 studies of food logs, and every one linked logging with more weight loss8. The authors call the evidence weak, because of how the studies were designed. But a log is still the simplest way to know your deficit is real.
Eating out takes more care, because a menu rarely shows the numbers in front of you. The nutrition pages list calories and protein for the big chains, and the high-protein fast food guide picks meals that fit a deficit.
Can you build muscle in a calorie deficit?
Yes, some people can. In a 2016 trial, young men ate about 40% under their needs for four weeks and trained six days a week with weights and intervals. The group that ate 2.4 g of protein per kilogram gained 1.2 kg (2.6 lb) of lean mass and lost 4.8 kg (10.6 lb) of fat. The group at 1.2 g/kg gained 0.1 kg of lean mass6.
That was a hard plan for four weeks, not a typical one. A 2020 review found the same kind of result in people who already lift, with progressive training and enough protein as the two keys9. If muscle is the main goal, read how to cut and how to lean bulk.
Why you are not losing weight in a calorie deficit
Most stalls have a plain cause. Your burn fell as you lost, your log missed some food, or water hid the loss for a week or two. The weight loss plateau post walks through each one. If the scale went up, read water weight before you change your plan.
Your calorie deficit in Fit Shapes
Your first target in the Fit Shapes app comes from this same formula. The app does not stop there. Adaptive Targets measures what you really burn from your food log and your weight trend, and proposes a new target each week. Fit Shapes also forecasts when you’ll reach your goal at your current pace, as a window of weeks, so the date moves as your real pace does.
Questions
Should I eat back the calories I burn when I exercise?
Not with this number. Your activity level already counts your usual workouts. If you add them again, you count them twice.
Why does this calculator use a different date than other calculators?
Each one makes its own guess about your burn and your pace. This page uses the same formula and the same straight line as the Fit Shapes app, and it calls the date an optimistic estimate. Your real burn falls as you lose, so the real date comes later.
Can I use this calculator if I am pregnant or breastfeeding?
No. Pregnancy and breastfeeding change how much energy you need, and this formula does not count that. Ask your doctor or a registered dietitian.
Can a teenager use this calculator?
No. It is for adults 18 and older. For a younger person, ask a doctor or a registered dietitian.
Does this calculator save what I type?
Only in this browser tab, and only until you close it. The math runs in your browser, and nothing you type leaves it. The tab keeps your answers so that the other calculators can use them.
Sources
9 sources
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247. doi.org/10.1093/ajcn/51.2.241
- Hall KD, Sacks G, Chandramohan D, Chow CC, Wang YC, Gortmaker SL, Swinburn BA. Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011;378(9793):826–837. doi.org/10.1016/S0140-6736(11)60812-X
- Thomas DM, Martin CK, Lettieri S, et al. Can a weight loss of one pound a week be achieved with a 3500-kcal deficit? Commentary on a commonly accepted rule. Int J Obes. 2013;37(12):1611–1613. doi.org/10.1038/ijo.2013.51
- Centers for Disease Control and Prevention. Steps for Losing Weight. January 17, 2025. www.cdc.gov/healthy-weight-growth/losing-weight/index.html
- Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr. 2014;11:20. doi.org/10.1186/1550-2783-11-20
- Longland TM, Oikawa SY, Mitchell CJ, Devries MC, Phillips SM. Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial. Am J Clin Nutr. 2016;103(3):738–746. doi.org/10.3945/ajcn.115.119339
- Rolls BJ. The relationship between dietary energy density and energy intake. Physiol Behav. 2009;97(5):609–615. doi.org/10.1016/j.physbeh.2009.03.011
- Burke LE, Wang J, Sevick MA. Self-monitoring in weight loss: a systematic review of the literature. J Am Diet Assoc. 2011;111(1):92–102. doi.org/10.1016/j.jada.2010.10.008
- Barakat C, Pearson J, Escalante G, Campbell B, De Souza EO. Body recomposition: can trained individuals build muscle and lose fat at the same time? Strength Cond J. 2020;42(5):7–21. doi.org/10.1519/SSC.0000000000000584