How many calories should I eat to lose weight?
A method that gives you your number, worked through for three body sizes, plus the scale check that tells you whether it is right.
How many calories to lose weight: the method
The honest answer is a method, not a number. Your target is your total daily energy expenditure (TDEE) minus a deficit of 10 to 25%. Two people the same height can need targets 800 kcal apart because of weight, age, sex and activity, which is why a single "eat 1,500 calories" answer is wrong for most of the people who read it.
- Estimate your BMR with the Mifflin-St Jeor equation: 10 × kg + 6.25 × cm − 5 × age, then +5 for men or −161 for women.
- Multiply BMR by an activity factor: 1.2 sedentary, 1.375 light, 1.55 moderate, 1.725 active, 1.9 very active. That gives TDEE.
- Subtract 10 to 25% of TDEE. Around 20% is a sensible default.
- Check the result against the floors below. If it falls under them, use a smaller deficit.
- Eat at that target for three weeks and compare weekly weight averages. Adjust from the data.
How low is too low? The calorie floors
A common guideline is not to eat below about 1,200 kcal per day for women or 1,500 kcal per day for men without medical supervision. Below those levels it becomes hard to get enough protein, fiber and micronutrients from food, and hunger and fatigue climb quickly. These are floors, not targets. Plenty of people lose weight well at 1,600 or 2,200 kcal because that is where their math lands.
If your calculated target lands under the floor, do not force it. Reduce the deficit to 10 to 15% instead, or add activity to raise TDEE. If you have a medical condition, take medication that affects appetite or weight, or notice signs of disordered eating, talk to a doctor or registered dietitian before setting any target.
Worked examples for three body sizes
Each example uses a 20% deficit. The arithmetic is shown so you can swap in your own numbers.
| Person | BMR (Mifflin-St Jeor) | TDEE | 20% deficit target |
|---|---|---|---|
| Woman, 60 kg (132 lb), 163 cm (5 ft 4 in), 40 years, light activity | 600 + 1,018.75 − 200 − 161 = 1,258 | 1,258 × 1.375 = 1,730 | 1,730 − 346 = 1,384 kcal |
| Man, 85 kg (187 lb), 180 cm (5 ft 11 in), 30 years, moderate activity | 850 + 1,125 − 150 + 5 = 1,830 | 1,830 × 1.55 = 2,837 | 2,837 − 567 = 2,270 kcal |
| Woman, 100 kg (220 lb), 168 cm (5 ft 6 in), 45 years, sedentary | 1,000 + 1,050 − 225 − 161 = 1,664 | 1,664 × 1.2 = 1,997 | 1,997 − 399 = 1,598 kcal |
Look at the spread. The 60 kg woman lands at about 1,380 kcal, close enough to the 1,200 floor that she should not push the deficit past 20%. The 85 kg man can eat 2,270 kcal and still lose about 0.5 kg (1 lb) a week at first: 567 × 7 = 3,969 kcal per week, and 3,969 ÷ 7,700 = 0.52 kg. The 100 kg woman is sedentary, so her target of about 1,600 kcal is lower than many people expect for her size; adding daily walking would raise her TDEE and let her eat more while losing at the same rate.
How to check the number with the scale
The calculation is an estimate. The scale is the measurement. Run the check for three weeks before you change anything.
- Eat at your target and log everything, including oils, drinks and tastes while cooking.
- Weigh every morning after the bathroom, before food, and average each week.
- Compare week 1 to week 3. A 20% deficit should show roughly 0.5 to 1% of body weight lost per week; for the 85 kg man that is 0.4 to 0.85 kg.
- Losing faster than that, and feeling drained: raise the target by 100 to 200 kcal.
- Losing nothing after three weeks: the deficit is smaller than it looks on paper. Audit the log before cutting calories.
The audit matters because self-reports drift low. In one well-known study, people who believed they could not lose weight under-reported their intake by 47% on average and over-reported exercise by 51%. Nobody does that on purpose; it comes from untracked bites and generous portion guesses.
Photo logging in Cal.AI catches most of it, since you scan the plate before you eat, see each item and the meal total, and can fix a portion on the result screen. If you want to know how close the estimates get, read how accurate AI calorie counting is.
Why the number changes as you lose
A target that works at 100 kg is too generous at 85 kg. The body burns fewer calories as it shrinks, and research shows expenditure often falls a bit more than the new size alone predicts. The 3,500-kcal-per-pound rule overstates long-term loss for exactly this reason.
The fix is simple: rerun the method every 5 kg (11 lb) or every eight weeks, whichever comes first. The 100 kg woman at 90 kg recalculates to a BMR of 1,564, a TDEE of 1,877 and a 20% target of about 1,500 kcal, roughly 100 kcal lower than her starting target. The NIDDK Body Weight Planner models this decline over months if you want a longer projection.
What to do next
- Run the five steps with your own weight, height, age, sex and a realistic activity level. When in doubt, choose the lower activity level.
- Check your result against the 1,200 or 1,500 kcal floor and shrink the deficit if needed.
- Set protein at 1.2 to 1.6 g per kg of body weight so the calories you eat keep you full and protect muscle.
- Log for three weeks, weigh daily, compare weekly averages, then adjust by 100 to 200 kcal at a time.
- Recalculate every 5 kg lost. The right number today is the wrong number in three months.
Frequently asked questions
Is 1,200 calories a day enough to lose weight?
For most women it is below their TDEE, so yes, it creates a deficit, but it is also the common lower limit for eating without supervision. Many people who land there have picked too large a deficit. If your TDEE is 1,900, a 20% deficit gives about 1,520 kcal, which loses weight more slowly but is far easier to sustain.
How many calories should I eat to lose 1 kg a week?
About 7,700 kcal below maintenance per week, or 1,100 kcal per day. That is only reasonable if your TDEE is high enough that the target stays above 1,200 to 1,500 kcal, which usually means a larger, active person. For most people 0.5 kg (1 lb) per week, from a 500 to 550 kcal daily deficit, is the sustainable rate.
Do I need to eat back the calories I burn exercising?
Not if your activity multiplier already includes your workouts, which it does if you chose light, moderate or active. Eating back tracker estimates on top of that counts exercise twice. If you link Apple Health in Cal.AI, you choose whether burned calories are added to the budget; leaving it off is the safer default.
Why do I lose weight fast in week one and then slow down?
The first week includes water. Lower carbohydrate intake drains some glycogen, and each gram of glycogen holds roughly 3 g of water, so a kilogram or two can leave in days. After that you see true fat loss, which is slower and steadier. Judge progress from week two onward using weekly averages.
Sources
- Mifflin MD, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. PubMed
- Lichtman SW, et al. Discrepancy between self-reported and actual caloric intake and exercise in obese subjects. N Engl J Med. 1992;327(27):1893-1898. PubMed
- Hall KD, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011;378(9793):826-837. PubMed
- National Institute of Diabetes and Digestive and Kidney Diseases. Body Weight Planner. NIDDK
Related articles
- How to set a calorie deficit you can actually keep
- How to calculate your TDEE (and what to do with the number)
- How to count calories with a photo: a step-by-step guide
- How fast should you lose weight? Safe, realistic rates by body weight
- 12 calorie-tracking mistakes that stall weight loss
