Minimum Calories per Day
Without a health professional supervising you, don't eat fewer than about 1,200 calories a day if you're a woman or 1,500 if you're a man (Harvard Health). Those are floors, not targets: your own target is your maintenance minus a moderate deficit, which for most adults sits well above them.
These floors are the safety rails under any calorie deficit diet: a line not to cross on your own, not a goal to reach.
The floors
For unsupervised dieting, Harvard Health Publishing puts the minimum at 1,200 calories a day for women and 1,500 for men. They are deliberately simple cutoffs: they don't scale with your body size, so a bigger or more active person's actual target sits far above them. They mark the bottom of what's sensible without medical oversight, not what anyone should aim for. Our calculators never plan a target below them — check where your own maintenance lands with the TDEE calculator.
What eating 1,500 calories a day does
Because the floors are flat, "1,500 a day" means very different things to different people. Here is what a flat 1,500-calorie intake would do to six adults (age 40, low active) — the deficit it creates, the weight the NIH model expects them to lose, and when they'd reach the bottom of the healthy range for their height if they kept it up:
| Starting point | Maintenance | Deficit | Wk 4 | Wk 13 | Wk 26 | Wk 52 | Reaches floor |
|---|---|---|---|---|---|---|---|
| Woman, 5 ft 4 in, 150 lb | 2,194 | 694 | 6.2 | 15.0 | 25.6 | 40.6 | ~week 56 |
| Woman, 5 ft 4 in, 180 lb | 2,359 | 859 | 7.2 | 17.6 | 30.6 | 50.6 | ~week 105 |
| Woman, 5 ft 4 in, 210 lb | 2,525 | 1,025 | 8.2 | 20.2 | 35.7 | 60.5 | ~week 149 |
| Man, 5 ft 10 in, 180 lb | 2,844 | 1,344 | 11.9 | 30.2 | reached the floor | reached the floor | ~week 25 |
| Man, 5 ft 10 in, 220 lb | 3,115 | 1,615 | 12.9 | 33.1 | 58.8 | reached the floor | ~week 46 |
| Man, 5 ft 10 in, 260 lb | 3,386 | 1,886 | 14.2 | 36.7 | 65.6 | 113.0 | ~week 65 |
For the men, 1,500 a day is a deficit of roughly 1,300 to 1,900 calories — beyond the 500-to-1,000 range Harvard Health describes, and the kind of aggressive cut covered in is a 1,000-calorie deficit safe. And for every one of the six, eating 1,500 a day indefinitely eventually takes them below a healthy weight for their height. That's the key point: a floor is for a cut, not a permanent plan. Recalculate as you lose, and let the calorie deficit calculator reset your target. A gentler, sustainable pace is the one in our 500-calorie deficit results.
Below the floor: very-low-calorie diets
Eating under about 800 calories a day is a very-low-calorie diet. In a one-year study of a commercial weight-loss program, people on a roughly 500-calorie-a-day diet were about three times as likely to need hospital care for gallstones as people eating 1,200 to 1,500 a day, though the absolute risk was low in both groups (Johansson et al. 2014). Losing weight very quickly can raise gallstone risk more generally (NIDDK). Below the floors is territory for a health professional's supervision, not a solo project (Harvard Health).
Is the floor the same for everyone?
The cutoff is the same for every adult, and that is exactly why it isn't a personal target: it doesn't mean you need that little. A larger or more active person needs far more, and eating to the floor would leave them in a steep, hard-to-sustain deficit. If you're pregnant or breastfeeding, or under 19, don't use these numbers at all — get medical advice, because your needs are different and these cutoffs weren't drawn for you.
If you're trying to eat as little as you can
If you find yourself trying to eat as little as possible, or eating feels out of control, please talk to a doctor or another health professional. That's not a failure of willpower, and it's not something you have to sort out alone — support helps in ways that trying harder on your own usually can't.
Frequently asked questions
What is the minimum number of calories a woman should eat?
About 1,200 a day without a health professional's supervision.
What is the minimum for a man?
About 1,500 a day without a health professional's supervision.
Is 1,500 calories a day enough?
It depends on your maintenance: for the 150-lb woman it's a 694-calorie deficit; for the 180-lb man it's 1,344 — beyond the range Harvard Health describes.
Will I lose weight eating 1,500 calories a day?
Almost every adult in the examples does, quickly at first; recalculate as you go so you don't drop below a healthy weight.
What happens if I eat under 800 calories a day?
That's a very-low-calorie diet; in one large study gallstone problems were about three times as common as at 1,200 to 1,500 a day, so it belongs under medical supervision.
Sources
- Harvard Health Publishing, Calorie counting made easy
- Johansson K et al., International Journal of Obesity 2014
- NIDDK, Gallstones
- Hall KD et al., The Lancet 2011 (NIH author manuscript)
- National Academies (2023), Dietary Reference Intakes for Energy, Table S-1
- National Academies (2023), chapter 7, activity levels
- CDC, Adult BMI categories