Calorie deficit calculator for weight loss
A calorie deficit means eating less than you burn. The calculator works out your burn with the Mifflin-St Jeor equation (1990) and takes 250, 500 or 750 kcal a day off it, which is roughly 0.25, 0.5 or 0.75 kg a week, but never more than 20% of your burn. For example, a 30-year-old woman, 165 cm, 70 kg, lightly active, gets 1,562 kcal a day at the moderate pace: 500 kcal is more than a fifth of her burn, so the deficit is trimmed to 391 kcal. For protein, fat and carbs at that target, use the macro calculator.
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Where the number comes from
The formula, a worked example and where it stops working
What is a calorie deficit
To lose weight, eat below your maintenance number (TDEE) by the size of your deficit. The calculator takes 250, 500 or 750 kcal a day off it. A kilogram of fat is usually counted as about 7,700 kcal (the same ratio as in the NHLBI guidelines, 1998), so that works out to roughly 0.25, 0.5 or 0.75 kg (about 0.55, 1.1 or 1.65 lbs) a week. An example from the calculator: a 30-year-old woman, 165 cm, 70 kg, lightly active, maintains on about 1,950 kcal and loses 0.25 kg a week on about 1,700. The calculator never takes more than 20% off maintenance; that cap is our cautious choice.
A calorie deficit means you burn more energy than you eat, and your body covers the gap from its reserves, fat tissue first. The maths is simple: 500 kcal a day × 7 days = 3,500 kcal, roughly 0.45 kg (1 lb) of fat a week. The 7,700 kcal per kilo figure is a rule of thumb, not a law of nature: in the first weeks the scale often drops faster because of water, then slows down.
The maintenance number the deficit is subtracted from comes from the Mifflin-St Jeor equation — Mifflin MD, St Jeor ST et al., American Journal of Clinical Nutrition, 1990, derived from 498 healthy adults aged 19-78 with energy expenditure measured by indirect calorimetry.
The long version — with reference tables for each rate of loss, a section on plateaus and the usual mistakes — is in the article what a calorie deficit is and how to calculate yours. If you want a step-by-step start, there is a plan for your first week. And if the weight stops coming off even though you are in a deficit, the reasons are covered in why you are not losing weight on a calorie deficit.
How to calculate a calorie deficit yourself, in four steps
The calculator does this instantly, but the maths is easy to follow on paper. Same woman as above: 30, 165 cm, 70 kg, working out 1-3 times a week.
The numbers match the calculator and the chart below. Where the first number comes from is covered in the BMR calculator, and the activity multipliers are explained in the TDEE calculator.
- Step 1. Basal metabolic rate (BMR) with the Mifflin-St Jeor equation: 10 × 70 + 6.25 × 165 − 5 × 30 − 161 ≈ 1,420 kcal. That is her burn at complete rest.
- Step 2. Total daily burn (TDEE, BMR × activity): 1,420 × 1.375 ≈ 1,953 kcal. Eat that much and her weight stays put.
- Step 3. The deficit: for 0.25 kg a week it is 1,953 − 250 = 1,703 kcal. For 0.5 kg you would take off 500, but that is 26% of her burn, above the 20% cap. So the calculator takes 20%: 1,953 − 391 = 1,562 kcal, about 0.36 kg a week.
- Step 4. The sanity check: 1,562 is above her BMR (1,420) and above the 1,200 kcal floor. If she wants it easier, the mild pace is 250 kcal off, about 13% of her burn.
How many calories to eat at each pace: women
The table runs the same maths as the calculator above for a range of weights. The first number column is your daily burn, which is also your maintenance level. The rest is what to eat per day to lose 0.25, 0.5 or 0.75 kg a week.
Look at the 60 kg row: at 0.5 and 0.75 kg a week the target is the same, 1,452 kcal. Both deficits are more than 20% of her burn, so the calculator trims them to the cap. For a smaller person the fast pace ends up slower than it says on the label.
| Weight | Burn (TDEE) | 0.25 kg/wk | 0.5 kg/wk | 0.75 kg/wk |
|---|---|---|---|---|
| 60 kg | 1,815 | 1,565 | 1,452 | 1,452 |
| 70 kg | 1,953 | 1,703 | 1,562 | 1,562 |
| 80 kg | 2,090 | 1,840 | 1,672 | 1,672 |
| 90 kg | 2,228 | 1,978 | 1,782 | 1,782 |
| 100 kg | 2,365 | 2,115 | 1,892 | 1,892 |
| 110 kg | 2,503 | 2,253 | 2,003 | 2,002 |
Kcal per day. Woman, 30, 165 cm, light activity (×1.375). The target never drops below 1200 kcal. The same maths as in the calculator.
How many calories to eat at each pace: men
Same table for a man. In the Mifflin-St Jeor equation men get +5 and women −161, so at the same weight, height and age a man's BMR is 166 kcal higher. The man in this table is also taller, which is why his column sits about 340 kcal a day above the women's.
The calculator's floor for men is 1,500 kcal (NHLBI, 1998), and the deficit cap is the same 20% of burn. If you fall between two rows, just put your own numbers into the form above.
| Weight | Burn (TDEE) | 0.25 kg/wk | 0.5 kg/wk | 0.75 kg/wk |
|---|---|---|---|---|
| 60 kg | 2,155 | 1,905 | 1,724 | 1,724 |
| 70 kg | 2,293 | 2,043 | 1,834 | 1,834 |
| 80 kg | 2,430 | 2,180 | 1,944 | 1,944 |
| 90 kg | 2,568 | 2,318 | 2,068 | 2,054 |
| 100 kg | 2,705 | 2,455 | 2,205 | 2,164 |
| 110 kg | 2,843 | 2,593 | 2,343 | 2,274 |
Kcal per day. Man, 30, 178 cm, light activity (×1.375). The target never drops below 1500 kcal. The same maths as in the calculator.
Which pace to pick
Pick a pace by how many weeks you can actually eat that way, not by how fast you want it gone. A slow deficit you keep for months beats a fast one that ends in a binge in week two.
- Mild (-0.55 lbs/week, 250 kcal a day in the calculator) — if you only have a little to lose or you're new to counting. Portions barely change, and you can keep it up for a long time.
- Moderate (-1.1 lbs/week) — a workable choice for a lot of people. For a smaller person 500 kcal is more than 20% of maintenance and the calculator trims it, so check the table above.
- Aggressive (-1.65 lbs/week) — makes sense with a lot to lose, and only for a while. The calculator still never takes more than 20% of your burn. If hunger starts running your day, step down to moderate.
Why eating below your BMR is a bad idea
BMR is what your body burns at complete rest: breathing, heartbeat, brain, body temperature. The calculator shows it in the result next to your target. Common practice is to keep a deficit target no lower than BMR, because going under it means eating less than you'd burn lying in bed all day.
Compare the two numbers in your result. If your deficit target came out below BMR, pick a gentler pace or add some movement, so the gap comes from burning more rather than from an emptier plate. For a 30-year-old woman at 165 cm and 60 kg, the formula gives a BMR of about 1,320 kcal. Without the cap, 0.5 kg a week would put her at 1,315, below BMR. With the 20% cap the calculator gives 1,452, and the mild pace is still the calmer pick.
Separately, the calculator never goes below 1,200 kcal for women or 1,500 for men (1,400 and 1,600 from age 60; the minimum follows NHLBI, 1998, the 60+ floor is our choice), and it warns you when it hits that floor. Treat it as the bottom of the maths, not as a target.
Not sure how much you need to lose in the first place? The BMI calculator shows the healthy weight range for your height using WHO cut-offs. If you're only a couple of kilos away, the mild pace is plenty. To see the date you'd reach your goal at each pace and your weight week by week, use the weight loss date calculator.
When to recalculate
Weight sits right inside the formula: every kilo you lose takes 10 kcal off your BMR, and with light activity your daily burn drops by about 14 kcal. Minus 5 kg is roughly 70 kcal, minus 10 kg roughly 140. So every 4-5 kg, enter your new weight and take the fresh number.
If the scale hasn't moved for two or three weeks, check your log and recalculate before you cut food further. Unlogged snacks, cooking oil and drinks are what usually eat a deficit. And if you'd rather burn more than eat less, walking is worked out in the calories burned walking calculator.
How we calculate
The formulas and limits are the same as in the CalCash bot: the site and the bot run the same code. Here is what goes into the number.
- Resting burn (BMR) — the Mifflin-St Jeor equation: 10 × weight in kg + 6.25 × height in cm − 5 × age, plus 5 for men or minus 161 for women (Mifflin MD, St Jeor ST et al., American Journal of Clinical Nutrition, 1990).
- Daily burn (TDEE) — BMR × an activity factor from 1.2 to 1.9. The idea of "BMR × physical activity level" comes from FAO/WHO/UNU, Human energy requirements, chapter 5, 2004. The 1.2–1.9 numbers themselves are the factors calculators commonly use; we could not trace their original source, so we do not pin them on anyone.
- Weight loss — minus 250, 500 or 750 kcal a day depending on pace, but never more than 20% of your burn. The 500 kcal step is the low end of the 500–1,000 kcal a day deficit in the NHLBI guidelines, 1998; 250 is gentler still. The 20% cap is our cautious choice, not a number from a study: we could not find a verified source for an exact percentage.
- Minimum while losing weight — 1200 kcal for women and 1500 for men, the top ends of the 1000–1200 and 1200–1500 kcal ranges in NHLBI, Clinical Guidelines on Overweight and Obesity in Adults, 1998. From age 60 the calculator keeps 1400 and 1600; that is our cautious choice. If your burn is below the minimum, the target equals your burn: eating more than you burn makes no sense when losing weight.
- Pace in kilograms — deficit × 7 days ÷ 7700 kcal per kilogram, the same ratio as in the NHLBI guidelines, 1998: a deficit of 500–1,000 kcal a day gives 1–2 lb (0.45–0.9 kg) a week. It is a rule of thumb: in the first weeks you also lose water.
A deficit only works if you actually hold it, and that means seeing what you ate. The simplest way is to let a bot that counts calories from a photo do the counting — it remembers your target and shows how much is left for today.
Frequently asked questions
Is losing 2 lbs a week safe?
Depends on where you start and how you feel. The fastest pace in the calculator is 0.75 kg (about 1.65 lbs) a week, and it makes sense with a lot to lose and only for a while. With less to lose most people pick 0.25-0.5 kg a week: on that deficit it is easier to eat enough protein and keep going for months. Losing faster than 1 kg a week is something to do with a doctor, not on your own: the NHLBI guidelines, 1998 talk about 1–2 lb (0.45–0.9 kg) a week.
Can I dip below my BMR?
Better not. BMR is what your body burns at complete rest, and common practice is to keep a deficit target no lower than that. Compare the two numbers in your result: if the target came out below BMR, pick a gentler pace. Separately, the calculator never goes below 1,200 kcal for women or 1,500 for men, the top ends of the ranges in NHLBI, 1998.
How do I calculate my calorie deficit?
Work out your total daily burn (TDEE): your Mifflin-St Jeor BMR times an activity multiplier. Take 250, 500 or 750 kcal off it, which is roughly 0.25, 0.5 or 0.75 kg a week, but no more than 20% of your burn. Then check the result is not below your BMR. The calculator on this page does every step at once, and a worked example with numbers is above.
How big should a calorie deficit be?
The calculator uses 250, 500 or 750 kcal depending on pace, but never more than 20% of maintenance. The 20% cap is our cautious choice: we could not find a verified source for an exact percentage. For a smaller person 500 kcal can easily be more than 20%, so look at the share of your burn, not just the number.
What if I am not losing weight on a deficit?
First check that everything is logged: snacks, cooking oil, drinks and weekends are what usually eat a deficit without you noticing. Then recalculate for your current weight, because a lighter body burns less and the old number may no longer be a deficit. Judge by your average weight over 2-3 weeks, not a single morning. The full breakdown is on the blog, in the article on not losing weight on a calorie deficit.
Reminders
Water and weight