How many calories do I need a day?
Short answer
Most adults need somewhere between 1,600 and 3,000 calories a day. The 2020–2025 U.S. Dietary Guidelines estimated 1,600 to 2,400 for women and 2,000 to 3,000 for men, depending on age, body size and activity. For a personal number, estimate your resting energy with the Mifflin–St Jeor equation, then multiply it by an activity factor between 1.2 and 1.725.
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What decides how many calories you need?
Your body spends energy in three ways: keeping you alive at rest, digesting food, and moving. Resting energy is the largest share for most people. Digesting a mixed diet uses about 5 to 15 percent of daily energy, and more when meals are high in protein, according to a 2004 review of diet-induced thermogenesis.
Movement varies the most from person to person. It includes exercise, but also walking, standing and fidgeting through the day, which researchers call non-exercise activity thermogenesis. People with manual jobs burn far more this way than people who sit most of the day.
That is why two people of the same weight can need very different amounts. The current 2025–2030 Dietary Guidelines put it simply: the calories you need "depend on your age, sex, height, weight, and level of physical activity."
How do you work out your daily calories?
Start with resting energy, then scale it by how active you are. The most widely validated formula for resting energy is the Mifflin–St Jeor equation. It was published in 1990 from measurements of 498 healthy adults aged 19 to 78, including people at a normal weight and people with obesity.
- Men: 10 × weight in kg + 6.25 × height in cm − 5 × age in years + 5
- Women: 10 × weight in kg + 6.25 × height in cm − 5 × age in years − 161
Multiply the result by the activity factor that fits your usual week. The product is your maintenance estimate: the calories that would keep your weight steady.
| Your usual week | Factor | Women's equation | Men's equation |
|---|---|---|---|
| Resting only | – | 1,450 | 1,620 |
| Mostly seated: little structured activity | 1.2 | 1,740 | 1,940 |
| Some movement: light activity 1–3 days a week | 1.375 | 2,000 | 2,220 |
| Regular exercise: moderate activity 3–5 days a week | 1.55 | 2,250 | 2,510 |
| Very active: hard activity most days | 1.725 | 2,500 | 2,790 |
How accurate is the estimate?
It's a good starting point, not a measurement. A 2005 systematic review compared the four equations most used in practice and found Mifflin–St Jeor the most reliable: it came within 10 percent of measured resting energy for more people, with and without obesity, than any other. The same review warned that older adults and U.S. ethnic minorities were underrepresented in the studies, and that errors for individuals can still be large.
The best check is your own trend. If your weight holds steady over a few weeks at a given intake, that intake is close to your real maintenance number, whatever the formula said.
What changes if I want to lose or gain weight?
Eating below your maintenance estimate creates a deficit, and eating above it creates a surplus. The old rule that a pound of weight equals 3,500 calories is only a rough fit. A 2008 analysis found it roughly matches people with more body fat but overstates the deficit needed per pound for leaner people.
Your needs also move as your weight moves. Weight is part of the formula, so as you lose weight your maintenance number falls, and the same intake leaves a smaller deficit than it did at the start.
Common questions
Is Mifflin–St Jeor right for everyone?
No single equation is. It was built from healthy adults aged 19 to 78, so it is less reliable for teenagers, very muscular people and anyone whose medical condition changes their metabolism. Needs also rise during pregnancy and breastfeeding. For women who start at a healthy weight, the 2020–2025 Dietary Guidelines estimated about 340 extra calories a day in the second trimester and 452 in the third, so talk to a clinician about your own number.
Why does my number change when my weight changes?
Each kilogram adds 10 calories to resting energy in the formula, and the activity factor scales that up further. Recalculate after a meaningful change in weight or activity so your target keeps matching your body.
Should I eat back the calories I burn exercising?
Not if your activity factor already counts that exercise. Adding a tracker's exercise estimate on top counts the same activity twice. SeeMeEat never adds exercise calories back to your target for this reason.
Sources
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition. 1990;51(2):241–247. pubmed.ncbi.nlm.nih.gov
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association. 2005;105(5):775–789. pubmed.ncbi.nlm.nih.gov
- U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020–2025, Appendix 2: Estimated Calorie Needs. web.archive.org
- U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2025–2030. cdn.realfood.gov
- Westerterp KR. Diet induced thermogenesis. Nutrition & Metabolism. 2004;1(1):5. pubmed.ncbi.nlm.nih.gov
- Levine JA. Non-exercise activity thermogenesis (NEAT). Best Practice & Research Clinical Endocrinology & Metabolism. 2002;16(4):679–702. pubmed.ncbi.nlm.nih.gov
- Hall KD. What is the required energy deficit per unit weight loss? International Journal of Obesity. 2008;32(3):573–576. pubmed.ncbi.nlm.nih.gov
Estimates, not medical advice. If you're pregnant, have a medical condition or have a history of disordered eating, talk to a clinician before changing how you eat.
Written by the SeeMeEat editorial team under a pen name.