A calorie deficit is when you take in less energy over a day than your body spends. Your body covers the gap from its own reserves — fat tissue first. You can calculate it by hand in three steps: basal metabolism from the Mifflin-St Jeor equation, times an activity multiplier, minus a deficit of 250-500 kcal that's no more than 20% of your burn. For a 30-year-old woman at 70 kg and 165 cm with light activity, that's about 1,950 kcal of burn and 1,562-1,703 kcal a day in a deficit, per our calorie deficit calculator. Enough for the scale to move, and still enough food that you don't quit by the weekend.
Eating "clean" and nothing happens
A familiar story: grilled chicken, brown rice, steamed broccoli, green smoothies with spinach and chia seeds. Three months later the scale hasn't budged.
Take an example: a 35-year-old man, 5 ft 10 (178 cm), 207 lb (94 kg), two workouts a week. Our calorie calculator puts his burn at about 2,590 kcal a day. Rice is fine food, but 300 g of dry brown rice is about 1,100 kcal by USDA FoodData Central. Add the oil in the pan and "just a few" nuts, and clean food easily runs past what he burns.
Here's the part that gets skipped: weight loss is arithmetic. Not willpower, not vibes, not a broken metabolism. If you eat more than you burn, you gain. Eat less, you lose. The clean food was fine. There was just too much of it.
How to calculate your calorie deficit
First you need your TDEE — total daily energy expenditure. Start from BMR using the Mifflin-St Jeor equation.
For men: BMR = (10 x weight in kg) + (6.25 x height in cm) minus (5 x age) + 5
For women: same thing, but minus 161 instead of plus 5.
The equation itself was published in Mifflin MD, St Jeor ST et al., American Journal of Clinical Nutrition, 1990, derived from 498 healthy adults aged 19 to 78 whose energy expenditure was measured by indirect calorimetry.
Then multiply by your activity level. Desk job all day — times 1.2. Light workouts 1-3 times a week — times 1.375. Serious training 3-5 times a week — times 1.55.
The idea of multiplying resting metabolism by an activity factor comes from FAO/WHO/UNU, Human energy requirements, chapter 5, 2004. The exact multipliers differ a little between calculators — they're a working convention, not a law of physics.
Quick example. A woman at 70 kg, 165 cm, 30 years old, working out twice a week lands around 1950 kcal a day. Taking 500 off would give 1453, but that's more than 20% of her burn, and the CalCash calculator doesn't cut deeper than 20%. So her target is about 1560. That's not starvation — it's a normal day of food with slightly smaller portions.
Or skip the arithmetic: the calorie deficit calculator does the same thing in three seconds — sex, age, height, weight, activity, pace, and you get your daily number. If you just want maintenance with no deficit, use the calorie calculator. And to see a rough date for reaching your goal, plus your weight week by week, try the weight loss calculator.
How to calculate your deficit by hand from your own log
The formula is an estimate. There's a more accurate way, and all it takes is a food log and a scale.
- For two weeks, eat the way you normally do and log everything, drinks and cooking oil included.
- Weigh yourself every morning before eating and work out the weekly average.
- Add up the calories for all 14 days and divide by 14. That's your average intake.
- If your average weight in week two is about the same as in week one, that average intake is your maintenance. Take 250-500 kcal off it, but no more than 20%, as the deficit calculator does, and you have your deficit.
Example. Two weeks add up to 30,800 kcal, so 2,200 a day, and the weight barely moved. Maintenance is about 2,200 kcal. Minus 500 would be 1,700, but 20% of 2,200 is only 440, so by the calculator's rule it's 2,200 − 440 = 1,760 kcal a day.
If your weight went up over those two weeks, your maintenance is below your average intake; if it went down, it's above. In that case use the formula number as a start and correct it against the scale two weeks later.
How much weight does a calorie deficit take off?
You count the deficit in calories per day, but you want to see it in pounds or kilos. The rough conversion: by a common estimate, which our calculator uses too, a kilo of body weight is about 7,700 kcal, or 3,500 per pound. The same ratio is behind the NHLBI clinical guidelines, 1998: a deficit of 500 to 1,000 kcal a day for 1 to 2 lb a week. So 500 kcal a day below maintenance is 3,500 kcal a week, about 0.45 kg or roughly 1 lb.
It's only an estimate. The first weeks go faster because of water, later weeks slower because your burn drops along with your weight. That's why a deficit isn't a one-time calculation: you redo it for your new weight every few kilos.
How much to eat at each rate of loss
Here are the numbers already worked out, using the same engine as the calculator on this site.
Women:
| 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 |
Woman, 30, 165 cm, light activity (×1.375). The deficit is capped at 20% of your burn and the target never drops below 1200 kcal. Worked out with the calorie deficit calculator.
Men:
| 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 |
Man, 30, 178 cm, light activity (×1.375). The deficit is capped at 20% of your burn and the target never drops below 1500 kcal. Worked out with the calorie deficit calculator.
Notice that for women up to 100 kg and men up to 80 kg, the 0.5 and 0.75 kg columns are the same. That's the 20% cap: the calculator won't take the deficit deeper even if you pick the fast pace. The cap is our own cautious choice, not a rule from a study.
Treat these as a reference point for an average height and age, not as your personal number. Change the age, height or activity level and the numbers move — run your own in the calculator. And if you want fat and carbs alongside the calories, there are tables for that as well: daily macro requirements.
How big should your deficit be?
This is where people go wrong. They see the math, get excited, and cut their intake in half. "I need 2000, so I'll eat 1000." Heroic — for three days. Then comes the crash, the pizza and the self-loathing.
The CalCash calculator offers three paces:
- 250 kcal a day, about 0.25 kg (half a pound) a week: comfortable, slow, you barely notice it. Good if you only have a little to lose. Not sure how much that is? The BMI calculator shows the healthy weight range for your height.
- 500 kcal a day, about 0.5 kg (1 lb) a week: the bottom of the 500-1,000 kcal range in the NHLBI guidelines.
- 750 kcal a day, about 0.75 kg a week by the same NHLBI ratio: if your burn is high.
In all three the deficit stays within 20% of your burn, and the target never goes below 1,200 kcal for women or 1,500 for men, the upper ends of the NHLBI low-calorie ranges (1,000-1,200 and 1,200-1,500). The CDC notes that people who lose weight gradually, about 1 to 2 pounds a week, are more likely to keep it off. Cutting harder mostly means being hungry for longer and more likely to quit.
One thing that matters more in a deficit than in normal life: protein. It's what keeps muscle on you while fat comes off. For people who train, the International Society of Sports Nutrition Position Stand, 2017 puts the useful range at 1.4-2.0 g per kg of body weight a day, and notes that a calorie deficit may call for more. What that comes to in grams at your weight, and how to hit it with ordinary food, is here: how much protein per day.
Why the type of diet doesn't matter
Keto, intermittent fasting, paleo, carnivore, Whole30 — they all work for exactly one reason. They create a calorie deficit, just through different tricks.
On keto you cut carbs, so you eat less. On IF you cut a meal, so you eat less. On paleo you drop packaged food, so you eat less again.
That's also why "I switched to healthy eating and gained weight" is such a common story. 100 g of almonds is 579 kcal, per USDA, about a third of the daily target for a small woman with a desk job. Healthy? Sure. But there's no deficit, and your body doesn't care how wholesome the food was.
How to hold a deficit day to day
Working out the deficit is half the job. The other half is not eating it back through drinks, snacks and weekends. That's practice rather than arithmetic, so it has its own day-by-day guide: how to stick to a calorie deficit for weight loss in your first week.
When the scale stops moving
If your weekly average holds flat for several weeks (in practice people usually look at two or three), that's a plateau. Normal, and usually fixable. The short version is below; the full breakdown of causes is in why you're not losing weight on a calorie deficit.
First, check whether you're still actually in a deficit. Most plateaus are unlogged calories, not a broken metabolism.
Second, recalculate for your current weight. Drop 6 kg and your burn is lower than it was — your old target may not be a deficit anymore.
Third, if you've been cutting for months, spend a couple of weeks at maintenance and then go back down. Long uninterrupted deficits are hard to hold, more mentally than physically.
What not to do: cut harder. That's the fastest route to a blowout. If you want the number to move, adding movement is easier: an hour of walking at an average pace burns about 196 kcal above rest at 70 kg, by our walking calculator (3.8 METs from the 2024 Compendium of Physical Activities). The calories burned walking calculator works it out for your weight, pace and time.
How to not crash and burn after a week
The classic mistake is dropping everything at once. Yesterday 2500, today 1200. Three days later you're eating peanut butter out of the jar at midnight.
Do it gradually instead. Take off a little each week; that's common practice, not a figure from a study. Eat slightly less than usual this week, a bit less again next week, and so on until you hit your target. By week three you're where you wanted to be and it hardly feels like a diet.
And track what you eat — specifically, not "roughly around 1500, I think." With the CalCash bot you send a voice note — "pasta with a meatball and a side salad" — and get the calories and macros back in a second. It's a Telegram bot that counts calories from a photo, with nothing extra to install. When the real numbers are in front of you, the decisions make themselves: the extra snack drops off the list once you can see you're at 1900 out of 2000.
Where to start in practice
If you want steps rather than theory, there's a separate walkthrough: a calorie deficit for weight loss, day by day through week one. It covers what to do on day one, what to eat through the week, and what to do when the scale stalls.
The short version: get your number from the calorie deficit calculator or take 250-500 kcal off your maintenance (no more than 20%), start logging food today, and judge progress by weekly averages instead of morning swings.
Reminders
Water and weight