How many calories a day do you need to lose weight

Your target minus 15-20%

To lose weight you need to eat about 15-20% less than your body burns, which for most women comes to 1,400-2,000 kcal a day and for most men 1,700-2,500 kcal. The exact number depends on your weight, height, age and how much you move.

Plenty of people are surprised by these numbers, since magazine diets of the nineties taught everyone that you lose weight on 1,000-1,200. On 1,200 people do lose weight fast for the first two weeks, but then they break down, lose muscle and gain it all back, while a moderate deficit works more slowly but can be kept up for months, and what goes is mostly fat.

How to find your target

Your target is how much energy your body uses in a day, and most of it, 60-70%, goes on basal metabolism, meaning breathing, the heart, the brain and keeping warm, even if you spend the whole day in bed with a book. The rest goes on movement, not just workouts but the walk to the bus stop, cleaning and standing at the stove, and about 10% of what you eat is spent on digesting it.

Basal metabolism is calculated with the equation Mark Mifflin and Sachiko St Jeor derived in 1990 from weight, height, age and sex, and then multiplied by an activity factor, from 1.2 for a sedentary life to 1.55 and above for people who move a lot. That gives your maintenance target, at which your weight stays the same, and for weight loss you take 15-20% off it.

The easiest way is to enter your details into the calorie calculator, which does all of this for you. How the formula itself works and where it goes wrong we'll cover separately with three real examples.

Table: how much to eat to lose weight

If you'd rather not calculate, or want a rough idea first, here are ready-made numbers. The calculation is for age 35: women 165 cm tall, men 178 cm. The weight-loss number uses a 15% deficit, as in our calculator.

Women, age 35, height 165 cm

Men, age 35, height 178 cm

How to choose your column:

• sedentary - office, car, no or almost no workouts;
• some movement - 1-3 workouts a week or lots of walking, 8-10 thousand steps a day;
• active - 4-5 workouts a week or physical work.

If you're under 35, add roughly 60-80 kcal for every 10 years, and if you're older, take off the same, while every extra 10 cm of height adds about 75-95 kcal. If you can't decide on a column, pick the one to the left: almost everyone overestimates their activity, and one workout a week with a desk job is still closer to "sedentary". It's better to start lower and add a little after a couple of weeks if you're losing too fast than to spend a month standing still.

Why too big a deficit backfires

The most famous experiment with a harsh deficit took place in Minnesota in 1944. Physiologist Ancel Keys fed 36 volunteers about 1,570 kcal a day for six months, and by the end they had lost around a quarter of their weight, along with their strength, their interest in anything but food and their ability to think about anything else. Once the limits were lifted, many ate 5,000 kcal a day and within a few months gained back more than they had lost, with fat returning first and muscle taking longer.

The same thing happens to ordinary people on a 1,000 kcal diet, only on a smaller scale. With a sharp deficit the body readily gives up muscle, which is costly to maintain, and less muscle means a lower metabolism and harder weight loss from then on, something high protein and strength training only partly prevent. Energy use falls further than weight loss alone would explain, because people move less, feel cold and go sluggish, which scientists call adaptive thermogenesis. Above all, after a couple of hungry weeks nearly everyone breaks and eats a week's savings over one weekend, then feels guilty on top of it.

The arithmetic is simple: a 400 kcal deficit kept up for 12 weeks gives about 5 kg of fat, while a 1,000 kcal deficit that turns into overeating after two weeks gives almost nothing. How to hold a deficit without breaking is covered in A calorie deficit without relapses.

How much you lose per week

The figure "1 kg of fat is about 7,700 kcal" comes from a 1958 paper by Max Wishnofsky, who put a pound of fat at 3,500 kcal. By that rule a 500 kcal daily deficit gives about 0.45 kg a week and 300 kcal about 0.3 kg. In reality it's a bit less, because your energy use falls as you get lighter, and in 2011 Kevin Hall of the US National Institutes of Health showed in The Lancet that the old rule noticeably overestimates weight loss over the long run.

The first week usually looks better on the scale, minus 1-2 kg, but that's mostly water and glycogen rather than fat, and then the pace evens out. If you're losing 1.5-3 kg a month, things are going as they should.

When to recalculate your target

It's worth updating your target after roughly every 4-5 kg you lose, because a lighter body burns less, and a number that gave you a deficit at 85 kg may not do so at 78 kg. Recalculate as well when your activity changes, if you changed jobs or started or stopped training, and if your weight has stalled for more than three weeks of honest counting. In that last case the formula has probably overestimated you: a formula is a guess, not a measurement, and if you log your food honestly and weigh yourself regularly, after a few weeks you can work out your real energy use from how much you ate on average and how your weight changed. MyFoodMate AI does this for you, and the Progress screen suggests adjusting your target when your data differ from the formula by more than 8%, as described in the guide Recalculating your target.

FAQ

You don't need to eat back workout calories if you chose your activity level with your training in mind, since they're already in your target, and fitness trackers often overstate the burn by 20-40% anyway, so adding everything your watch shows is a sure way to lose your deficit. If you eat below your target and still don't lose weight, the counting is almost always off, with oil, drinks, snacks or weekends left out, and less often the formula overestimated your energy use, which a week of honest logging will reveal. And you can eat different amounts on different days, since what matters is the weekly average: eat a little less on weekdays and a little more at the weekend, and as long as the average stays on target, you'll see results.

Sources

1. Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990.
2. Hall KD et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet, 2011.
3. Rosenbaum M, Leibel RL. Adaptive thermogenesis in humans. International Journal of Obesity, 2010.
4. Wishnofsky M. Caloric equivalents of gained or lost weight. American Journal of Clinical Nutrition, 1958.

MyFoodMate editorial team

We check blog materials against current WHO recommendations.