Free calorie deficit calculator
How big a deficit, and how long it will take.
Most calculators hand you a daily number and stop. This one also sizes the deficit against the rate you picked, works out how many weeks it implies, and prints the month you would get there — then tells you where that estimate is optimistic, because it is.
General wellness guidance, not medical advice. If you are pregnant, breastfeeding, under 18, or managing a medical condition, talk to a doctor or a registered dietitian before acting on any of these numbers.
The arithmetic, in three lines
Maintenance comes from Mifflin–St Jeor times your activity factor — the TDEE calculator shows that step in full. The deficit is your chosen weekly rate times 7,700 calories per kilogram, divided by seven. Your daily target is maintenance minus that, floored at 1,200.
| Weekly rate | Daily deficit | Who it suits |
|---|---|---|
| 0.25 kg | ~275 kcal | Already lean, or protecting hard training |
| 0.5 kg | ~550 kcal | The default that most people can actually hold |
| 0.75 kg | ~825 kcal | Reasonable above roughly 90 kg |
| 1.0 kg | ~1,100 kcal | Only sustainable at a high starting weight, and rarely for long |
Where the estimate goes wrong
Maintenance is a moving target. Every kilogram you lose lowers what your body costs to run, so a fixed daily target is a shrinking deficit. Over a long cut this is the difference between the date the arithmetic promised and the date you actually arrive.
Adaptation is real but usually overstated. Expenditure falls a little more than mass alone explains — mostly because you move less without deciding to. It is a hundred or two, not the metabolic shutdown the internet describes.
The first fortnight lies in both directions. Fast at the start because of water and glycogen, then apparently stalled when that water comes back. Neither is fat changing at that speed.
All three have one fix, and it is not a better calculator: re-check the number against your real weight trend every few weeks. NutriLog AI does that continuously — it re-refines your target every time you log a weight and moves the projected date with it, so the plan tracks what your body is actually doing.
Protect the muscle while the fat goes
A deficit decides how much weight you lose. Protein and resistance training decide how much of it is fat. The protein calculator sets that target — it goes up in a deficit, not down — and the macro calculator splits the rest of the calories around it.
Common questions
How big should a calorie deficit be?
A useful default is 500 calories a day, which is about half a kilo — a pound — of fat a week. As a fraction, keeping weekly loss under roughly one per cent of your body weight keeps most of the loss as fat. That means a 100 kg person can run a much larger deficit than a 60 kg person without paying for it in muscle, which is why a flat "eat 1,200 calories" is bad advice for one of them and impossible for the other.
How long will it take to lose the weight?
Divide the weight you want to lose by your weekly rate. This calculator does that and prints a month. Treat it as the optimistic edge: maintenance falls as you get lighter, so the same daily target becomes a smaller deficit over time and the finish drifts later than the straight-line arithmetic suggests.
Is 1,200 calories a day safe?
It is the floor this calculator will not go below, and even reaching it should be deliberate rather than accidental. Below roughly 1,200 it becomes genuinely hard to hit protein, fibre and micronutrient needs from food, and adherence collapses. If the rate you picked would have pushed the target under the floor, the honest answer is to pick a slower rate, raise your activity, or talk to a doctor or registered dietitian — not to eat less.
Why did I lose 2 kg in the first week and then stop?
Because the first week is mostly not fat. Lower carbohydrate intake empties glycogen, and each gram of glycogen holds roughly three grams of water; gut contents fall too. It comes back the moment you eat normally for a day, which is why week two so often looks like a stall and is not one. Judge the trend over three to four weeks, never week to week.
What is 7,700 calories per kilogram?
The standard planning figure for the energy stored in a kilogram of body fat — 3,500 calories per pound. It is a simplification: real losses include some lean tissue and water, and the figure drifts as you get leaner. It is accurate enough to size a deficit and too crude to predict a specific day, which is why this page gives a month rather than a date.
Do I need to eat back the calories I burn exercising?
Not if your activity level above already describes your normal week — that would count the same training twice. And be sceptical of the calories your watch reports: consumer estimates for exercise burn are commonly a third too high, and eating all of them back is one of the most common ways a carefully planned deficit turns into maintenance without anyone noticing.
Other free calculators
The deficit is the easy half. Holding it is the other one.
NutriLog AI logs the food against this target in under a minute a meal, smooths your weight into a trend and moves the goal date as the real data arrives. Free, no ads, Android. Free on Google Play.