Calorie deficit calculator for weight loss
This calorie deficit calculator works out how many calories to eat to lose weight: it estimates your maintenance with the Mifflin-St Jeor formula, subtracts the deficit you choose and turns the result into a daily target, a weekly pace and an estimated date for your goal weight. Free, no sign-up, and nothing you type is stored.
What is a calorie deficit? A calorie deficit is the gap between the calories you eat and the calories you burn in a day. If your maintenance is 2,200 kcal and you eat 1,700, the deficit is 500 kcal. Held over time, the body covers that gap from stored fat, at 7,700 kcal per kilogram (3,500 per pound) by convention.
Your goal weight is at or above your current weight, so there is nothing to lose and no date to estimate. To maintain or gain weight, the TDEE calculator gives maintenance and surplus targets instead.
Your target has been held at the generally recommended minimum intake (1,200 kcal for women, 1,500 for men); when even your estimated maintenance is below that minimum, no target is shown. Going below it, or eating at a level this close to your estimated expenditure, should be supervised by a healthcare professional. The pace and date shown are the ones the held target actually delivers.
The deficit you chose comes to more than 1,000 kcal a day, above the 500 to 1,000 kcal range usually quoted for a loss of 1 to 2 lb (0.5 to 1 kg) a week. Deficits that large are hard to sustain and should be supervised by a healthcare professional.
| Deficit | Daily target | Weekly change | Weeks to goal |
|---|---|---|---|
| — | |||
† Target held at the minimum intake (1,200 kcal for women, 1,500 for men); the pace shown is the one the held target delivers. The bold row is the option selected above.
Values recalculate instantly as you type. Nothing is sent or stored — the math runs in your browser.
How the calculation works
The calculator first estimates your basal metabolic rate (the calories your body burns at complete rest) with the Mifflin-St Jeor equation and multiplies it by a factor for your activity level to get your maintenance calories. It then subtracts the deficit you chose, holds the result at the minimum intake if necessary, and converts the deficit that survives into a weekly pace and a linear estimate of the weeks and date to your goal weight.
Mifflin-St Jeor (1990, the most accurate for the general population):
Men: (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
Women: (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
Maintenance = basal metabolic rate × activity factor: 1.2 sedentary, 1.375 light, 1.55 moderate, 1.725 active, 1.9 very active.
Daily target = maintenance − deficit, where the deficit is a fixed 250, 500, 750 or 1,000 kcal or 10, 15, 20 or 25 % of maintenance, and the target is never taken below 1,200 kcal for women or 1,500 kcal for men.
Weekly change = deficit applied × 7 ÷ 7,700 kcal per kg of body fat (3,500 kcal per lb).
Weeks to goal = (current weight − goal weight) × 7,700 ÷ (deficit applied × 7); the estimated date is today plus that many days.
The equation comes from Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA and Koh YO, A new predictive equation for resting energy expenditure in healthy individuals, American Journal of Clinical Nutrition, 1990;51(2):241–247 (doi:10.1093/ajcn/51.2.241). The activity factors are the conventional multipliers used with that equation: a convention, not a measurement of you. If you prefer the revised Harris-Benedict equation (Roza AM and Shizgal HM, The Harris Benedict equation reevaluated, American Journal of Clinical Nutrition, 1984;40(1):168–182), the daily calorie calculator offers both. The 7,700 kcal per kilogram figure is Wishnofsky's 1958 estimate, the convention this site uses throughout; how many calories are in a pound of fat explains where it comes from and where it breaks. The 1,200 and 1,500 kcal floors are the intake levels below which supervision is generally recommended; 1,200 and 1,500 calorie diets traces where those numbers came from and who they are not for.
Limits of the estimate
The weeks and the date are a linear estimate that real bodies do not follow. As you get lighter, the weight term in the equation shrinks and your maintenance falls with it, so a fixed calorie target delivers a smaller deficit every month; the early weeks also include water and glycogen that come back. The date is therefore the earliest plausible finish under perfect arithmetic, not a forecast. Re-run the calculator with your new weight every few pounds or kilograms, and expect the last stretch to be the slowest.
Every formula is a statistical estimate: your real number varies with body composition, genetics and metabolic adaptation. Because the Mifflin-St Jeor constant is 166 kcal lower for women and their average maintenance is lower, a fixed 750 or 1,000 kcal deficit reaches the 1,200 kcal floor far more often for women; the percentage options scale with your own maintenance instead. A floor is a limit, not a target. The estimate is not valid during pregnancy or breastfeeding (it does not account for the energy that breastfeeding takes), for people under 18, for elite athletes or with metabolic conditions — in those cases the reference should come from a healthcare professional. The way to refine the number is to log what you eat for two or three weeks and compare it with how your weight actually moves.
Frequently asked questions
How can I figure out my calorie deficit?
Estimate your maintenance calories (this calculator multiplies the Mifflin-St Jeor equation by an activity factor), then subtract what you eat. If maintenance is 2,250 kcal and you eat 1,750, the deficit is 500 kcal a day. The only way to check the estimate is to log your intake for two or three weeks and compare it with how your weight actually moves.
How much of a deficit do you need to be in to lose 2 lbs a week?
By the 3,500 kcal per pound convention, 2 lb a week is 7,000 kcal a week, or 1,000 kcal a day below maintenance. For many people, and most women, that lands below the 1,200 or 1,500 kcal floor, so the calculator holds the target there and shows the slower pace the held target actually delivers.
How long does it take to lose 20 pounds on a 500 calorie deficit?
Twenty pounds is about 70,000 kcal at 3,500 per pound. At 500 kcal a day that is 140 days, roughly 20 weeks, if the deficit stayed constant. It does not: expenditure falls as you get lighter, so the real figure is longer. Re-run the calculator with your new weight every few pounds.
What is a good calorie deficit for a female?
The arithmetic is the same for everyone, but women's maintenance is usually lower, so a fixed 750 or 1,000 kcal deficit more often breaches the 1,200 kcal floor. A percentage option (10 to 25 % of maintenance) scales with your own number: at 2,000 kcal, 20 % is 400 kcal a day, about 0.8 lb a week.
How can I lose 20 pounds in 2 months as a female?
Twenty pounds in about 61 days is 70,000 kcal divided by 61, a deficit near 1,150 kcal a day. That is above the 1,000 kcal a day upper end usually quoted and, for most women, below the 1,200 kcal floor, so this calculator will not produce it. At 500 to 750 kcal a day the linear estimate is 13 to 20 weeks. A faster plan needs professional supervision.
How many calories should I eat to lose weight?
Your maintenance minus a deficit you can keep. This calculator estimates maintenance from sex, age, height, weight and activity, then subtracts 250 to 1,000 kcal or 10 to 25 % of it. For a 30-year-old woman of 70 kg and 170 cm with moderate activity, maintenance is about 2,250 kcal and a 500 kcal deficit gives 1,750 kcal a day.
Which calorie deficit calculator is the most accurate?
None of them measures you: every calculator applies a population formula. Mifflin-St Jeor is the equation this page and most others use because its 1990 paper found the older Harris-Benedict equations overestimated measured expenditure. The accurate number is the one you calibrate: log what you eat for two or three weeks, compare with the scale, and adjust the target by the difference.
Keep reading
How many calories are in a pound of fat? · 1,200 and 1,500 calorie diets: where the numbers came from · How many calories should I eat per day? · Daily calorie calculator with macros · Protein calculator
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