📉 Calorie Deficit Calculator
Work backwards from the weight you want and the date you want it by, to the daily deficit that requires. It also tells you when that target is asking for more than is sensible.
Working backwards from a target to a daily number
Most calorie calculators start from a deficit and tell you the outcome. This one runs the other way: you set the weight and the date, and it tells you what that requires, then says whether the requirement is sensible. The second part matters more than the first, because the arithmetic will happily produce a target nobody could sustain.
daily deficit = (kg to lose × 7,700) / (weeks × 7)
The 7,700 is the approximate energy content of a kilogram of body fat, about 3,500 calories per pound. It is a convenient constant and a slight simplification, because real weight loss includes some water and lean tissue.
What different deficits actually mean
| Deficit | Daily intake | Weekly loss | Sustainability |
|---|---|---|---|
| 10% | 2,160 | 0.22 kg | Very easy to hold, slow |
| 15% | 2,040 | 0.33 kg | Comfortable |
| 20% | 1,920 | 0.44 kg | The usual recommendation |
| 25% | 1,800 | 0.55 kg | Demanding but workable |
| 30% | 1,680 | 0.65 kg | Hard to hold, more muscle lost |
Percentages work better than fixed numbers. A 500-calorie deficit is 20% for someone burning 2,500 and 33% for someone burning 1,500. The second person will struggle and lose more muscle doing it, even though the number on the page is identical.
The rate that keeps the muscle
Around 0.5% to 1% of body weight a week is the range most evidence supports. Below that, progress is slow enough to lose motivation. Above it, an increasing share of the loss comes from lean tissue rather than fat, and the steeper the deficit the worse that ratio gets. For an 85 kg person, 1% is 850 g a week; for a 60 kg person it is 600 g, which is why absolute targets like "a kilo a week" are much harsher for smaller people.
Two things reliably protect lean mass in a deficit: enough protein, at 1.6 to 2.2 g per kg of body weight, and resistance training two or three times a week. Neither is optional if you care what the weight you lose is made of.
Why the deficit shrinks as you go
A smaller body costs less to run. Lose 8 kg and your maintenance falls by roughly 100 to 150 calories a day, so the intake that produced a 500-calorie deficit now produces a 370-calorie one. On top of that, spontaneous movement falls during a diet without people noticing, which can be worth another 100 to 200 calories. Together they explain almost every stall at the three-month mark.
The fix is to recalculate every four or five kilograms rather than holding one number for the whole journey. The TDEE calculator gives the updated maintenance figure.
Floors worth respecting
Below roughly 1,200 calories for women and 1,500 for men, getting adequate protein and micronutrients becomes genuinely difficult, and adherence collapses. If the arithmetic demands a figure below that, the honest answer is not to eat less but to extend the timeline or raise activity. A target that requires an unsustainable intake is a target that will not be reached.
A worked example
An 82 kg woman, 168 cm, 34, lightly active, wanting 72 kg in 20 weeks. Her maintenance is 2,116 calories. Losing 10 kg in 20 weeks requires a 550-calorie daily deficit, so an intake of 1,566, which is 26% below maintenance and at the steep end. Stretching the target to 26 weeks drops the required deficit to 423 calories and the intake to 1,693, which is a 20% deficit and far easier to hold for six months.
This page explains published formulas and population averages. It is general information, not medical advice, and it cannot account for your individual health.
Once you have this figure, the TDEE calculator is where it usually goes next. the calorie calculator is the related one people reach for afterwards.
Frequently Asked Questions (FAQs)
How big should a calorie deficit be?
Fifteen to twenty-five per cent below maintenance for most people, producing roughly 0.5% to 1% of body weight lost per week. Larger deficits lose more muscle and are abandoned more often, which makes them slower in practice than they look on paper.
How many calories are in a kilogram of fat?
About 7,700, or 3,500 per pound. It is an approximation: real weight loss includes water and some lean tissue, so the scale usually moves faster than the fat alone at the start and slower later.
Why did my weight loss stall?
Three things compound: maintenance falls as you get lighter, spontaneous movement drops during a diet, and intake tends to drift upward without being logged. Recalculate your maintenance, log honestly for a week, and judge by the weekly average rather than daily readings.
Can I lose weight faster safely?
Up to about 1% of body weight a week, yes, with adequate protein and resistance training. Beyond that the proportion of muscle lost rises sharply, and very aggressive deficits require medical supervision to remain safe.
Should I eat back exercise calories?
Partly at most. Trackers overestimate burn by 20% to 30%, and if your activity multiplier already reflects your training then those calories are counted once. Eating back half of what a device reports is a reasonable compromise.
Is a 1,200 calorie diet too low?
For most adult women it is the practical floor, and for men it is around 1,500. Below those levels, meeting protein and micronutrient needs becomes difficult and adherence drops. If your target demands less, extend the timeline instead.