How many calories to lose weight

Start from what you burn

A deficit is defined against your maintenance, so you need that first. The TDEE calculator will estimate it from your height, weight, age, sex and activity — bearing in mind, as that page says, that the estimate is a population average and yours may sit a few hundred calories either side.

Once you have it, the deficit is a percentage of it rather than a fixed number, because a 500 kcal cut means something very different to someone maintaining at 3,000 than to someone maintaining at 1,700.

A useful sanity check is 0.5–1% of body weight per week. For a 200 lb person that is 1–2 lb; for a 130 lb person it is 0.65–1.3 lb. The same percentage, very different absolute numbers — which is exactly why two people should not compare their weekly results.

The 3,500-calorie rule, and why it overpromises

You will have met this one: a pound of fat is about 3,500 kcal, so a 500 kcal daily deficit loses a pound a week. The energy content is roughly right. The prediction that follows it is not.

It assumes your expenditure stays fixed while you shrink, and it does not. As you lose weight there is less of you to move and to maintain, so maintenance falls. Sustained dieting also tends to reduce spontaneous movement — you fidget less, walk a little slower, take the stairs less often — without any conscious decision. Both effects erode the deficit you set. This is well documented: the rule was derived from the energy content of tissue alone and ignores the adaptations that follow weight change, so it systematically over-predicts loss.¹ Modelling the dynamics instead produces a plateau, with weight responding on a half-time of roughly a year.²

The practical consequence: a deficit that produced a pound a week in month one produces noticeably less by month three, at the same intake. This is not failure and it is not a broken metabolism. It is the arithmetic changing underneath a plan that was written once and never revisited. It is also precisely the case that adaptive targets exist to handle.

How low is too low

Aggressive deficits are tempting and mostly counterproductive. What tends to go wrong:

• More of the loss comes from muscle, especially without enough protein and resistance training. You end up lighter but not the shape you were aiming for.
• Adherence collapses. The best deficit is not the largest one, it is the largest one you will still be doing in three months.
• Training quality falls, which removes the main signal telling your body to keep the muscle.
• Micronutrients get hard. Below roughly 1,200 kcal it is genuinely difficult to cover requirements from food.

Commonly cited floors are around 1,200 kcal a day for women and 1,500 for men, and those are floors rather than targets. Very low calorie diets below that exist as a clinical tool used under medical supervision, which is a different thing from a decision you make on your own.

Reading the results without panicking

Two weeks in, the scale will have done something confusing. It always does. Water, sodium, glycogen and your cycle move daily weight by several pounds, which is often larger than a fortnight of genuine fat loss — so judge the smoothed trend, over weeks, not any single morning.

If the trend genuinely has not moved in two to three weeks, check consistency of logging before you cut calories. A gradual drift in how carefully you measure looks exactly like a stall and is far more common than a metabolic one.

A worked example

Maintenance estimated at 2,400 kcal. A 20% deficit is 1,920 — call it 1,900. Body weight 180 lb, so protein at roughly 1.8–2.2 g/kg lands around 150–180 g. That leaves about 1,200 kcal for carbs and fat, split however you actually enjoy eating.

Three weeks later, the trend has fallen about 2.5 lb — a shade under a pound a week, which is on target. Two more weeks and it flattens: expenditure has come down with the weight. The fix is a modest trim, roughly 100 kcal, not a dramatic cut. That cycle — measure, adjust a little, continue — is the whole method.

References

Every figure on this page traces to one of these. We checked each against the primary source rather than citing from memory; follow the links and hold us to them.

1. Thomas DM, Martin CK, Redman LM, et al. (2013). Why is the 3500 kcal per pound weight loss rule wrong?. International Journal of Obesity, 37(12):1611–1613. PMID 23628852 The 3,500 kcal rule assumes expenditure holds still while you shrink. It does not, so the rule systematically over-predicts how much weight a given deficit will remove.
2. Hall KD, Sacks G, Chandramohan D, et al. (2011). Quantification of the effect of energy imbalance on bodyweight. The Lancet, 378(9793):826–837. PMID 21872751 Weight responds to a change in intake slowly, with a half-time on the order of a year, and settles at a plateau rather than falling forever. Static models predict a straight line that real bodies do not follow.
3. Helms ER, Zinn C, Rowlands DS, Brown SR. (2014). A systematic review of dietary protein during caloric restriction in resistance trained lean athletes: a case for higher intakes. International Journal of Sport Nutrition and Exercise Metabolism, 24(2):127–138. PMID 24092765 In lean, energy-restricted, resistance-trained athletes, protein needs were estimated at 2.3–3.1 g per kg of FAT-FREE mass, rising with leanness and with the severity of the deficit.
4. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. (1990). A new predictive equation for resting energy expenditure in healthy individuals. The American Journal of Clinical Nutrition, 51(2):241–247. PMID 2305711 Derived from 498 healthy adults aged 19–78. This is the equation behind our TDEE calculator: 10×kg + 6.25×cm − 5×age, +5 for men and −161 for women.

Common questions

General wellness information, not medical advice — see our health disclaimer. Talk to a clinician before making significant dietary changes.