Calorie Deficit to Lose Weight: How Big Should It Be?

To lose weight at a pace you can keep up, set a calorie deficit that takes off about 0.5 to 1% of your body weight per week. For most adults that means eating roughly 300 to 500 calories a day below maintenance, and not going under about 1,200 calories a day for women or 1,500 for men without medical supervision. The calorie deficit calculator turns your weight and chosen pace into a daily number.

How to size your deficit

You need two numbers: your maintenance calories and the pace you want.

1. Find your maintenance. Estimate it with the TDEE calculator, then ideally confirm it with two or three weeks of weighing (the method is in maintenance calories).
2. Pick a pace. Choose a weekly loss as a percentage of your body weight. A review of nutrition for natural bodybuilders recommends setting intake so that body weight drops by about 0.5 to 1% a week (Helms, Aragon & Fitschen, 2014). The CDC puts it in pounds: people who lose about 1 to 2 pounds a week are more likely to keep the weight off (CDC).
3. Convert it to calories. One kilo of body weight is roughly 7,700 kcal (3,500 kcal per pound). Daily deficit = weekly loss in kg × 7,700 ÷ 7.

Harvard Health uses the same rule: a deficit of 500 calories a day for about a pound a week (Harvard Health).

A worked example

Made-up numbers: a woman who weighs 75 kg (165 lb) with a maintenance of 2,200 kcal a day.

For her, 0.5% a week is a sensible start. At 1% she is getting close to the 1,200 floor, and in a few months, as her maintenance drops, she would cross it. A heavier person has more room: at 110 kg, the same 0.5% is 0.55 kg a week and a deficit of about 600 kcal.

Why bigger isn't better

A larger deficit loses weight faster on paper, but there are costs.

In a study with 24 elite athletes who all lifted four times a week, one group dieted to lose 0.7% of body weight a week and the other 1.4%. Both lost about 5.5% of their weight. The slower group, eating about 19% less than usual, gained 2.1% lean body mass. The faster group, eating about 30% less, saw no change in lean mass (Garthe et al., 2011). These were athletes, so the exact numbers won't carry over to everyone, but the direction matches what the bodybuilding review recommends.

Bigger deficits are also harder to keep. Hunger, tiredness and worse workouts make it more likely you drop the plan after three weeks. A moderate deficit that lasts four months does more than an aggressive one that lasts four weeks.

There is also a floor. Harvard Health advises not going below 1,200 calories a day for women or 1,500 for men except under a health professional's supervision. If your numbers land below that, choose a slower pace or move more instead of eating less.

Why weight loss slows down

The 3,500-calories-per-pound rule assumes every pound you lose is the same mix of fat and lean tissue. A modelling paper showed it roughly fits people with more than 30 kg of body fat and overstates the energy per kilo for leaner people, who lose a larger share of lean tissue (Hall, 2008).

Your maintenance also drops as you lose weight, so the same intake gives a smaller deficit each month. In another model, the half time of weight change after a change in intake was about a year (Hall et al., 201160812-X)). That's why the straight line in any calculator is a best case. A plateau after two or three months usually means the deficit has shrunk, not that your body has stopped responding.

What to do:

• Recalculate maintenance every 4 to 5 kg lost and set a new target.
• Compare weekly averages, not daily weigh-ins. Water and salt can hide a week of fat loss.
• Before cutting food again, check your logging and your daily steps. Small gaps add up.

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Protect your muscle while you diet

Two habits make most of the difference:

• Keep lifting. Strength training gives your body a reason to keep muscle while you eat less. See strength training for weight loss for how to set it up.
• Eat enough protein. Protein needs go up in a deficit. The protein calculator gives a target for dieting, and high protein foods for muscle building lists what to eat to reach it.

Don't expect a deficit to build much muscle at the same time. A 2022 meta-analysis of resistance training trials found that people training in an energy deficit gained less lean mass than people training without one, while their strength gains were similar. In its pooled model, a deficit of around 500 kcal a day was enough to stop lean mass gains, and the authors advise people who want to keep muscle while losing weight to stay below that (Murphy & Koehler, 2022). For the 75 kg woman in the example above, that points to the 0.5% pace rather than 0.75% or 1%. For many people, holding on to muscle during a diet is a fair goal, and adding it comes later.

Your strength in the gym is a useful check. If your main lifts hold steady or improve, the deficit is probably fine. If they drop week after week, slow the pace.

Diet breaks: does stopping help?

A diet break means eating at maintenance for a week or two before going back into a deficit. The best-known trial is the MATADOR study. Men with obesity were split into two groups. One dieted continuously for 16 weeks. The other did the same 16 weeks of dieting in two-week blocks, with two weeks at maintenance between each block, so the plan took 30 weeks. Intake during the diet blocks was 67% of maintenance in both groups (Byrne et al., 2018).

During the maintenance blocks, weight barely moved, so the breaks didn't undo the progress. The trial has clear limits: 47 men with obesity started the diet, 36 finished it as planned, no women took part, the deficit was large, and the version with breaks took almost twice as long. Treat breaks as an option for a long diet that is wearing you down, not as a trick that speeds things up.

Signs your deficit is too big

• You are hungry most of the day and thinking about food constantly.
• Your sleep, mood or energy has dropped noticeably.
• Your lifts keep going down.
• You lose more than about 1% of your body weight per week after the first couple of weeks.

If several of these apply, add 100 to 200 kcal back and see how the next two weeks go.

Who should get help first

This article is general information, not medical advice. If you are pregnant or breastfeeding, under 18, have diabetes or another medical condition, take medication that affects appetite or blood sugar, or have had an eating disorder, don't start a diet without a doctor or a registered dietitian.