Calorie Calculator: How Many Calories You Need Per Day

How many calories do you need per day?

Most adults need between 1,600 and 3,000 calories a day to hold their weight steady. Where you fall in that range depends on body size, sex, age, and how much you move. A 5 foot 2 inch woman who works at a desk might maintain on 1,700. A 6 foot 2 inch man who walks all day at work might need 3,000 or more.

The Dietary Guidelines for Americans publish average needs for reference adults: a man who is 5 feet 10 inches and 154 pounds, and a woman who is 5 feet 4 inches and 126 pounds. Their table is a useful sanity check. It is not built for your height or weight, which is why this calculator starts from your own numbers instead.

Your result is called maintenance calories, the intake at which weight stays about the same. Every loss or gain target on this page is built from that number.

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How to use this calorie calculator

Weigh yourself in the morning, after using the bathroom and before eating, in light clothing. Measure height standing straight against a wall without shoes. Enter your age in whole years and the sex used for the equation.

Pick the activity level that matches a normal week, not your best week. Then leave the equation on Mifflin-St Jeor unless you have a reason to compare.

The calculator returns maintenance calories first, then targets for losing or gaining 0.5, 1, and 2 pounds a week, plus your resting calories. A target that falls below a common safety floor is marked. Treat every number as a starting point you will test against your scale over the next few weeks.

The equations behind the result

The calculator first estimates resting calories, the energy your body uses for breathing, circulation, and organ function while at rest. The default is the Mifflin-St Jeor equation from 1990. Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5. Women: the same, minus 161.

A 2005 systematic review by Frankenfield and colleagues compared the common prediction equations against measured resting metabolism. Mifflin-St Jeor was the most reliable of the group, landing within 10% of the measured value more often than the others in both nonobese and obese adults.

The second option is the Harris-Benedict equation as revised by Roza and Shizgal in 1984. It tends to run 50 to 150 kcal higher than Mifflin-St Jeor for the same person. It is offered so you can see how much your answer depends on the choice of equation.

Resting calories are then multiplied by an activity factor, from 1.2 for sedentary to 1.9 for extra active. The product is maintenance.

Worked example: a 35-year-old woman who is 165 cm (5 ft 5 in) and 70 kg (154 lb), moderately active. Mifflin-St Jeor gives 10 × 70 + 6.25 × 165 − 5 × 35 − 161 = 1,395 kcal at rest. Multiplying by 1.55 gives a maintenance estimate of 2,163 kcal a day. The revised Harris-Benedict equation gives 1,455 kcal at rest and 2,254 kcal maintenance, a difference of about 90 kcal.

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Choosing your activity level

Activity level moves the result more than anything else you enter. For the woman in the example, the same body gives anywhere from 1,674 to 2,651 kcal a day depending on the setting.

The Dietary Guidelines define sedentary as only the activity of independent living. Moderately active means the equivalent of walking 1.5 to 3 miles a day at 3 to 4 mph on top of that, and active means more than 3 miles. Those walking distances are a better yardstick than how hard your workouts feel.

When two levels both seem to fit, choose the lower one. Your weight trend will tell you within a month if it was too low.

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Reading your weight loss and gain targets

The loss and gain targets use the old rule of thumb that a pound of body weight equals about 3,500 kcal. Eating 500 kcal a day under maintenance creates a 3,500 kcal weekly gap, or roughly 1 pound a week. Eating 250 kcal under gives about half a pound.

For the example woman, that means about 1,913 kcal a day for half a pound a week, 1,663 for 1 pound, and 1,163 for 2 pounds. The last one falls under 1,200, so the calculator flags it.

The CDC notes that people who lose about 1 to 2 pounds a week are more likely to keep it off than people who lose faster. For most people, the 1 pound target is the place to start.

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Why weight loss slows on the same calories

The 3,500 kcal rule works for the first weeks and then overpromises. Thomas and colleagues showed that it predicts far more weight loss over a year than people actually lose, because it treats the calorie gap as fixed.

The gap does not stay fixed. As you lose weight, a smaller body burns fewer calories, so the same intake creates a smaller deficit each month. Hall and colleagues modeled this in adults and found that weight responds slowly to a lasting change in intake, with about half of the eventual change reached after roughly a year.

In practice, recalculate after every 10 to 15 pounds of change. Entering your new weight lowers maintenance and resets the targets. The NIDDK Body Weight Planner, built on the Hall model, can project the full curve if you want a date.

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Safe minimums and when to get help

The 2013 adult obesity guideline from the American Heart Association, American College of Cardiology, and The Obesity Society lists 1,200 to 1,500 kcal a day for women and 1,500 to 1,800 kcal a day for men as typical weight-loss diets, or a deficit of 500 to 750 kcal a day. This calculator flags loss targets under 1,200 kcal for women and 1,500 kcal for men.

Those floors are not personal minimums. A small, sedentary older woman may have a maintenance close to 1,500, so a 500 kcal cut puts her under the floor without being extreme for her size. Very low calorie diets can work under medical supervision. They are not a do-it-yourself plan.

Talk to a doctor or registered dietitian before cutting calories if you are pregnant or breastfeeding, take insulin or other glucose-lowering drugs, have kidney disease, or have a history of an eating disorder.

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How accurate is the estimate, and how to fine-tune it

Even the best equation misses some people by more than 10%. On a 2,200 kcal maintenance, that is a 220 kcal error in either direction, nearly half of a 500 kcal deficit.

Your own data fixes that. Eat close to one target for two to four weeks, weigh on most mornings, and compare weekly averages. If the average holds steady, that intake is your real maintenance. If you lose faster or slower than the target predicts, shift intake by 100 to 200 kcal and give it another two weeks.

Skip the bathroom scale for the first few days of a new plan. Water and stored carbohydrate swing early readings by a few pounds. A two-week average is the first number worth acting on.

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Who this calculator is not for

The equations were built from healthy adults. They are not validated for children or teens, whose needs include growth; the National Academies publish separate pediatric energy equations. Pregnancy and breastfeeding add calories that change by trimester and feeding pattern.

Very muscular athletes often burn more than predicted because the equations do not see muscle mass. Thyroid disease, recovery from illness or surgery, and some medications also change energy needs. In those cases, use the result as a rough guide and work with a clinician.

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How it works

Resting calories from Mifflin-St Jeor (or revised Harris-Benedict) × activity factor = maintenance. Weight-change targets subtract or add 250, 500, or 1,000 kcal/day, based on the 3,500 kcal per pound rule of thumb.

Frequently asked questions

• How many calories should I eat a day?Eat your maintenance number to hold weight steady. For gradual loss, start about 500 kcal below it, which the 3,500 kcal rule puts at roughly 1 lb a week in the first weeks. Real loss slows over time as your body gets smaller.
• Why does my result differ from other calorie calculators?Calculators use different equations and activity factors. Mifflin-St Jeor and revised Harris-Benedict can differ by 50 to 150 kcal for the same person, and choosing one activity level up or down changes the result by 10 to 15%.
• What is the lowest calorie intake that is safe?Adult obesity guidelines use 1,200 to 1,500 kcal a day for women and 1,500 to 1,800 kcal a day for men as typical weight-loss diets. Going lower should be supervised by a clinician.
• Is this calculator accurate for children or pregnancy?No. It uses adult equations. Children, teens, and pregnant or breastfeeding people need different estimates from a pediatrician, obstetric provider, or dietitian.

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References

1. Mifflin et al.. A new predictive equation for resting energy expenditure in healthy individuals
2. Roza and Shizgal. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass
3. Frankenfield et al.. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review
4. USDA/HHS. Dietary Guidelines for Americans, 2020-2025, Appendix 2: Estimated Calorie Needs
5. Hall et al.. Quantification of the effect of energy imbalance on bodyweight
6. Thomas et al.. Can a weight loss of one pound a week be achieved with a 3500-kcal deficit? Commentary on a commonly accepted rule
7. Jensen et al.. 2013 AHA/ACC/TOS guideline for the management of overweight and obesity in adults
8. CDC. Steps for Losing Weight
9. NIDDK. Body Weight Planner
10. National Academies. Dietary Reference Intakes for Energy