Calorie Calculator: How Many Calories Should I Eat?

How the calculator works

It is two steps. First it estimates your basal metabolic rate (BMR), the calories your body burns at rest to keep you alive. Then it multiplies that by an activity factor to cover everything else you do in a day: walking, working, training, digesting food. The result is your total daily energy expenditure, the same thing as maintenance calories.

The resting part is the Mifflin-St Jeor equation, published in 1990:

• Men: BMR = 10 × weight in kg + 6.25 × height in cm − 5 × age + 5
• Women: BMR = 10 × weight in kg + 6.25 × height in cm − 5 × age − 161

The paper fitted 9.99 per kg and 4.92 per year, rounded to 10 and 5 with no loss of accuracy. Pounds divided by 2.2046 give kilograms; inches times 2.54 give centimeters. The calculator does the conversion for you.

A worked example. A 35-year-old woman, 5 feet 5 inches (165.1 cm) and 150 lb (68.0 kg), who works at a desk and lifts three days a week, wants to lose fat.

The deficit comes from the old rule that a pound of body fat holds about 3,500 calories (7,700 per kilogram): 0.75 lb × 3,500 ÷ 7 days is 375 calories a day. That rule is a rough guide, which is one more reason the adjustment step below matters.

Picking your activity level

The activity factor moves the answer more than anything else you enter. The gap between sedentary and very active is over 40%, roughly 900 calories a day for an average man.

Most people pick one level too high. An hour of lifting burns less than it feels like: a lot of that hour is rest between sets. What moves your daily burn most is everything outside the gym, mainly steps. If you lift three times a week on a beginner gym plan and sit the rest of the day, start at light, not moderate. If you are torn between two levels, pick the lower one; the weigh-ins will tell you if you were wrong.

Setting the goal: lose, maintain or build

Lose fat. The calculator aims for about 0.5% of your bodyweight a week, which works out to 2.5 calories per pound of bodyweight a day, capped at 500. That is at the gentle end of the 0.5 to 1% a week that Helms and colleagues suggested for lifters who want to keep their muscle while they diet. Slower loss is easier to stick to and leaves more energy for training.

There is also a floor. The calculator will not set a fat-loss target under 1,200 calories a day for women or 1,500 for men, and if your maintenance is already near that, it suggests no deficit at all. Below those levels it gets hard to cover protein, vitamins and minerals from food. A small, sedentary woman can hit the floor fast: at 30 years old, 5 feet 2 inches and 120 lb, maintenance is about 1,460, so the normal 300-calorie deficit would land at 1,160 and the target stops at 1,200 instead. If you want to go lower, or you have diabetes, a heart or kidney condition, are pregnant or breastfeeding, or have a history of disordered eating, set the number with a doctor or registered dietitian.

Maintain. Eat the maintenance number. This is the right choice while you learn to lift, and it is the base for body recomposition, where beginners lose some fat and gain some muscle at the same weight.

Build muscle. Add 200 to 300 calories a day. The calculator uses 250. Aim for a scale trend of about 0.5 to 1% of bodyweight a month, toward the top end in your first year of lifting. Bigger surpluses mostly add fat faster, not muscle. The build muscle guides cover the training side.

How accurate is it?

When Frankenfield and colleagues compared the common resting-energy equations against measured values in 2005, Mifflin-St Jeor came out the most reliable: it landed within 10% of the measured number for more people than any other formula. But a sizable minority still sat outside that 10%, and the activity multiplier adds its own error on top. So read every result as a range. A maintenance of 2,500 means somewhere from about 2,250 to 2,750.

Things that push your real number away from the estimate:

• Muscle. The formula only knows weight, not what the weight is made of. A muscular lifter often burns more than predicted; someone with a high body fat level often burns less.
• Daily movement. Steps, fidgeting and standing vary by hundreds of calories between people with the same job. This is the biggest unknown.
• Dieting history. After a long diet, energy expenditure tends to drop more than weight loss alone explains. Hall and colleagues showed in 2011 that the 3,500-calorie rule overstates long-term loss for this reason.
• Food tracking. Most people under-report what they eat, often by a few hundred calories a day: oils, sauces, drinks and bites while cooking.
• Age. The formula takes off 5 calories a year. Much of the real drop with age comes from losing muscle and moving less, both of which lifting slows.

Fitness watches and gym machines estimate calories burned too, and they tend to read high. Do not add their numbers on top of an activity factor that already counts your training.

Adjust after two to three weeks of weigh-ins

The formula gives a starting number. Your scale gives the real one. Here is how to turn the first into the second.

1. Eat the target every day for two to three weeks, tracked as honestly as you can. Weekends count.
2. Weigh yourself at least three mornings a week, after the bathroom, before eating. Daily is better.
3. Compare weekly averages, not single days. Water, salt, carbs and the menstrual cycle move the scale 1 to 4 lb (0.5 to 2 kg) day to day. Ignore the first week of a diet, which is mostly water.
4. Adjust by the gap. Each 0.5 lb (0.25 kg) a week you are off target is roughly 250 calories a day.

Recheck every 10 to 15 lb (5 to 7 kg) of change, or run the calculator again with your new weight. As you lose weight, maintenance falls, so a deficit that worked at the start shrinks over time.

What to do with the number

A calorie target is only half the plan. What fills those calories, and what you do in the gym, decides whether you lose fat or muscle.

• Set protein first. About 1.6 g per kg of bodyweight (0.7 g per lb) a day, and up to 2.2 g/kg in a deficit. How much protein you need explains the range.
• Split the rest into carbs and fat. Keep fat at about 20 to 35% of calories and fill the rest with carbs. The macro calculator does the split in grams.
• Keep lifting heavy while you cut. The deficit takes away fat; heavy training tells your body to keep the muscle. Cutting without losing muscle covers how.
• Pick foods that fill you up. At 1,500 to 1,800 calories, volume and protein matter. The list of high-protein, low-calorie foods ranks them per 100 calories.

Questions people ask

How many calories should I eat to lose weight?

Your maintenance minus about 0.5% of your bodyweight a week, which is 2.5 calories per pound a day, and never more than 500 under maintenance. For most adults that lands between 300 and 500 a day.

What is the difference between BMR and TDEE?

BMR is what you burn lying still all day. TDEE adds everything you do, from walking to lifting. TDEE is the number you eat around; BMR is only the first step of the sum.

Should I eat back the calories I burn exercising?

No, if you picked an activity level that includes your training, which this calculator does. Adding exercise calories on top counts your workouts twice.

Why am I not losing weight at my calorie target?

Usually the target is about 10% too high for you, or tracking has drifted. Check two weeks of averages, tighten tracking, then cut 150 to 250 calories a day.

Is 1,200 calories a day enough?

For many women it is the lowest sensible target without medical supervision; for most men, 1,500 is. If the calculator stops at the floor, a doctor or dietitian can tell you whether going lower is safe.

Where these numbers come from

• Mifflin, St Jeor and colleagues, A new predictive equation for resting energy expenditure in healthy individuals (American Journal of Clinical Nutrition, 1990): the BMR equation.
• Frankenfield, Roth-Yousey and Compher, a systematic review comparing resting metabolic rate equations in healthy adults (Journal of the American Dietetic Association, 2005): Mifflin-St Jeor as the most reliable, and its 10% error band.
• Activity multipliers from 1.2 to 1.9: the standard factors used with BMR equations in dietetics texts. They are rounded conventions, not measurements of you.
• Helms, Aragon and Fitschen, evidence-based recommendations for natural bodybuilding contest preparation (Journal of the International Society of Sports Nutrition, 2014): losing 0.5 to 1% of bodyweight a week to keep muscle.
• Hall and colleagues, Quantification of the effect of energy imbalance on bodyweight (The Lancet, 2011): why the 3,500-calorie rule overstates long-term loss.

The deficit cap, the calorie floors and the adjustment table are our own rules of thumb, set on the cautious side. This calculator is for healthy adults and is not medical advice.