How Many Calories Should I Eat to Lose Weight?

Most adults lose weight at a steady pace when they eat about 500 kcal a day less than their body burns. The 2013 US obesity guideline recommends a daily cut of 500 to 750 kcal, or a fixed intake of 1,200 to 1,500 kcal for women and 1,500 to 1,800 kcal for men, adjusted for body weight. Your own number depends on your size, age and how much you move. All you need to work it out is your weight, height, age and a calculator.

Key takeaways

• Start from what you burn: resting energy times an activity factor.
• Eat about 500 kcal a day below that. A cut of 500 to 750 kcal is the range in clinical guidelines.
• Weight loss slows as you get lighter, so recalculate every few kilograms.
• Very low intakes (under about 800 to 1,200 kcal) need a doctor or dietitian.

Step 1: Estimate how many calories you burn

Your body burns energy all day, even asleep. The part you burn at rest is called resting energy expenditure. A widely used formula for it is the Mifflin-St Jeor equation, built in 1990 from measurements of 498 healthy adults:

Resting energy covers breathing, your heart and keeping warm. Walking, working and training come on top. To include them, multiply by an activity factor. The expert report on energy needs by the FAO, the WHO and the United Nations University groups daily life like this:

If you are unsure, pick the middle of your row, as the examples below do. If the scale does not move after a few weeks, try a factor nearer the bottom of the row.

Step 2: Take about 500 kcal off

Eating less than you burn is the part that makes weight come off. The US guideline lets doctors choose between three ways of eating less. One is a daily cut of 500 or 750 kcal. Another is a fixed intake of 1,200 to 1,500 kcal for women or 1,500 to 1,800 kcal for men. The third is a diet that limits certain foods, such as high-fat or high-carbohydrate foods.

A 500 kcal cut is a good default: big enough to show on the scale within a few weeks, small enough to live with. A 750 kcal cut moves faster and is harder to keep up. The NHS suggests aiming for 0.5 to 1 kg a week. Expect the first weeks to be faster than later ones, because a lighter body burns fewer calories.

Two worked examples

These are examples, calculated with the formula above, not real people.

A woman, 35, 168 cm, 70 kg, office job, walks most days. Resting energy: 10 × 70 + 6.25 × 168 - 5 × 35 - 161 = 1,414 kcal. Activity factor 1.55: about 2,190 kcal a day to stay the same weight. Target for weight loss: about 1,700 kcal a day.

A man, 40, 180 cm, 90 kg, office job, gym twice a week. Resting energy: 10 × 90 + 6.25 × 180 - 5 × 40 + 5 = 1,830 kcal. Activity factor 1.55: about 2,840 kcal a day to stay the same weight. Target for weight loss: about 2,340 kcal a day.

Both targets sit above the guideline ranges, which is normal for people who are taller, heavier or more active. The guideline itself says those fixed ranges are usually adjusted for body weight.

Step 3: Update the number as you lose weight

A lighter body burns fewer calories. Every kilogram you lose lowers the number from Step 1 a little, so the same intake gives a smaller and smaller deficit.

Kevin Hall at the US National Institutes of Health and colleagues measured how big this effect is. Their 2011 paper in The Lancet found that a lasting change of about 10 kcal a day moves body weight by about 1 pound (0.45 kg) in the end, with half of that change after about a year and nearly all of it after three years. For an average adult with overweight, a 500 kcal daily cut works out to roughly 11 kg in the first year, or about 0.2 kg a week on average. The old rule of thumb, 3,500 kcal per pound, promises about twice that, because it ignores how the body adapts. Slower progress after the first months is normal and does not mean the plan has failed.

To keep losing at a steady pace:

• Recalculate every few kilograms. Run Step 1 again with your new weight and set a new target.
• Judge your trend over several weeks, not single days. Water and salt move the scale up and down from one morning to the next.

The NIH also offers a free Body Weight Planner built on the same model, if you want a calculator that does the slowing for you. The research behind Cal Clark's calorie targets is on the science page.

How low is too low?

Eating very little does not make the process safer or easier. The NHS notes that very low calorie diets, under about 800 to 1,200 kcal a day, are not suitable or safe for everyone and should run with professional support. Below the guideline ranges, it gets hard to eat enough protein, fibre, vitamins and minerals, and hunger makes the plan hard to keep.

Talk to your doctor before you cut calories if you are pregnant or breastfeeding, under 18, have had an eating disorder, take medication for diabetes, or have a long-term health condition.

Making the number work in real meals

A target only helps if you know roughly what you eat. A systematic review of 22 studies found a consistent link between tracking food and losing weight, and a 2019 study in Obesity found that people who logged more often during the day lost more weight than people who logged less often.

Food records written from memory tend to come in low. In a small study in the New England Journal of Medicine, people who said they could not lose weight on a low intake under-reported what they ate by 47% on average. They wrote down only about half of it. Weighing food for a week or two, or logging each meal as you eat it, narrows that gap.

Cooking fat is easy to forget. One tablespoon of olive oil is about 13.5 g and about 120 kcal. When you log a meal from a photo, say how much oil you cooked with, because a camera often misses it. In Cal Clark you can add it as a short note with the photo. Oil and sauces are also where photo calorie estimates miss most.

Frequently asked questions

Should I eat back the calories I burn exercising?

Usually not. The activity factor from Step 1 already includes your regular exercise, so adding it again counts it twice. If you train hard on some days and not others, eating a little more on training days and a little less on rest days averages out to the same weekly total.

Is 1,200 calories a day enough?

For some smaller, less active women it can work for a while, and it is the bottom of the range in the US guideline. For most men and for active or taller women it is too low to keep up. Work out your own number with the steps above rather than starting from 1,200.

Why am I not losing weight on my calorie target?

Check three things first: portions that are bigger than you think, cooking oil and drinks that never get logged, and a target that has not been updated since you lost weight. Log everything for two weeks, weigh portions of rice, pasta, oil and cheese, and redo Step 1 with your current weight.

Sources

• Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr, 1990.
• FAO, WHO, UNU. Human energy requirements, chapter 5: physical activity levels. 2001.
• Jensen MD, Ryan DH, et al. 2013 AHA/ACC/TOS guideline for the management of overweight and obesity in adults. Circulation, 2014.
• NHS. Obesity: treatment.
• Hall KD, Sacks G, et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet, 2011.
• Burke LE, Wang J, Sevick MA. Self-monitoring in weight loss: a systematic review of the literature. J Am Diet Assoc, 2011.
• Harvey J, Krukowski R, et al. Log often, lose more: electronic dietary self-monitoring for weight loss. Obesity, 2019.
• Lichtman SW, Pisarska K, et al. Discrepancy between self-reported and actual caloric intake and exercise in obese subjects. N Engl J Med, 1992.
• USDA FoodData Central. Oil, olive, salad or cooking.