The Calorie Deficit You Need to Lose Weight, Explained

In brief: to lose weight, you need a calorie deficit: eating fewer calories than your body burns. A deficit of about 250 to 550 calories a day suits most people. It fits the NHS target of losing 0.5 to 1 kg (1 to 2 lb) a week. Start from your maintenance calories, subtract your deficit, and adjust after a few weeks based on how your weight actually changes.

What a Calorie Deficit Means

Your body burns a certain number of calories each day. That's your total daily energy expenditure, or maintenance calories. If you eat exactly that much, your weight stays roughly the same. If you eat less, your body makes up the shortfall from stored energy, mostly fat, and your weight comes down over time.

That shortfall is the calorie deficit. It is the common thread behind every successful weight-loss diet, whether it cuts carbs, fat or meal times. The diet is just the method you use to eat less.

How Big Should a Calorie Deficit Be to Lose Weight?

A moderate calorie deficit is the one most people can stick to. The NHS recommends losing weight steadily, at 0.5 to 1 kg (1 to 2 lb) a week. A common rule of thumb converts weekly goals into a daily deficit:

Weekly goal	Daily deficit (approximate)
0.25 kg (0.5 lb)	250–275 calories
0.5 kg (1 lb)	500–550 calories
0.75 kg (1.5 lb)	750–825 calories
1 kg (2 lb)	1,000–1,100 calories

The daily figures come from the idea that a kilogram of body weight stores about 7,700 calories, or a pound about 3,500. That's a useful starting estimate, but it's only a rule of thumb, as the next section explains.

Two guardrails help keep a deficit safe:

• Keep the pace within the NHS range. For lighter people, 1 kg (2 lb) a week is a large share of body weight. Our goal planner flags any pace above 1% of your body weight a week, as a prompt to check it suits you.
• Treat 1,200 calories a day as a floor unless you have medical support. The NHS describes diets under 800 or 1,200 calories a day as very low calorie diets. It warns that they don't suit everyone and can be unsafe for some people, and are usually only recommended, with support from a dietitian, when weight is affecting other health conditions.

The NIDDK, part of the US National Institutes of Health, suggests a first goal of losing 5% of your body weight across six months. For someone weighing 90 kg (198 lb), that's 4.5 kg (about 10 lb). That's slower than the maximum safe pace, and it's still a change that matters for health.

Why Weight Loss Slows Down

Many people find the scale moves fast in the first weeks and then slows, even though they're eating the same amount. That's expected, and it's not a sign that something is wrong.

• The 3,500-calorie rule is too simple. A 2008 analysis by NIH researcher Kevin Hall found it roughly matches the energy in lost weight for people starting with more than 30 kg of body fat. For leaner people, it overestimates the deficit needed per unit of weight lost, because a bigger share of what they lose is lean tissue, which holds less energy than fat. The same model predicts that the deficit needed per kilogram falls as weight loss goes on.
• Your burn falls as you shrink. A smaller body needs fewer calories, so the same intake becomes a smaller deficit over time. Hall's 2011 modeling in The Lancet found that body weight responds slowly to a change in intake, with a half-time of about a year. It also found that people with more body fat can expect to lose more weight from the same calorie cut.
• Daily weigh-ins are noisy. Your weight on any one morning reflects food, drink and fluid as well as fat. Judge progress by the trend over two to three weeks, not by single weigh-ins.

So if your loss slows after a few months, recalculate your maintenance calories at your new weight. The TDEE calculator updates the figure as soon as you change your weight.

A Worked Example

A 35-year-old woman, 165 cm (5 ft 5 in) and 70 kg (154 lb), exercises three to five days a week. Her estimated maintenance is about 2,160 calories a day. She wants to reach 64 kg (141 lb).

• Goal pace: 0.5 kg (about 1 lb) a week. That's under 1% of her body weight (0.7 kg).
• Daily deficit: 0.5 × 7,700 ÷ 7 = 550 calories
• Daily target: 2,160 − 550 = about 1,610 calories a day
• Time to goal: 6 kg ÷ 0.5 kg a week = about 12 weeks, likely a little longer as her burn falls.

Her target stays above 1,200 calories, and the pace is moderate. If she's losing faster than about 0.7 kg (1.5 lb) a week after the first fortnight, she can eat a little more. If she's losing nothing after three weeks, she can cut 100 to 200 calories. The calorie goal planner runs these numbers and gives a target date.

Calorie Deficit for Women and Men

The method is the same for everyone: maintenance minus deficit. The difference is in the numbers. The Dietary Guidelines estimates put most women's maintenance calories several hundred below men's. So the same 500-calorie deficit is a bigger share of a woman's intake, and it brings her closer to 1,200 calories a day. A smaller woman may need a slower pace, such as 0.25 kg (0.5 lb) a week, to keep her intake at a sensible level.

Hall's 2008 analysis also offers one reason men often lose weight faster on the same deficit. Women typically carry more body fat than men of the same weight, and the model predicts that people with more body fat need a larger deficit per kilogram lost.

How to Protect Muscle While You're in a Deficit

When you eat less, your body can lose muscle as well as fat. Two habits help you keep it:

• Eat enough protein. The International Society of Sports Nutrition says higher intakes may be needed to keep lean mass in trained people during a deficit. See how much protein you need a day for the ranges.
• Keep strength training. Muscle that's being used is far more likely to be kept.

Limits and When to Get Advice

Calorie estimates are a starting point, and real results vary. Speak to a doctor before starting a weight-loss plan if you are pregnant or breastfeeding, under 18, have diabetes or take medication that affects blood sugar, or have a history of disordered eating. A doctor can also discuss medical and specialist options if diet and activity alone haven't worked.

Frequently Asked Questions

Is a 1,000-calorie deficit too much?

For many people, yes. A 1,000-calorie daily deficit aims for about 1 kg (2 lb) a week, the top of the NHS range. People with a higher body weight and higher maintenance calories may manage it. For smaller people, it can push intake under 1,200 calories, into the range the NHS calls very low calorie.

Why am I in a calorie deficit but not losing weight?

The most common reasons are that maintenance calories were overestimated, or that intake is higher than it seems. Portion sizes, drinks and weekends add up. Water retention can also mask fat loss for a week or two. Track your intake carefully for two to three weeks, judge your weight trend, and lower your target by 100 to 200 calories if nothing moves.

Can I lose weight without counting calories?

Yes. Any approach that leaves you eating less than you burn will work, whether that's smaller portions, fewer snacks or more vegetables and protein. Counting calories simply makes the deficit visible and easier to adjust. Many people count for a few weeks to learn their portions, then switch to simpler habits.

How long should I stay in a calorie deficit?

Until you reach your goal, as long as the pace and intake stay within safe ranges. Hall's modeling shows weight responds slowly, so a large goal can take many months. Recalculate your maintenance every few kilograms. Once you reach your goal, move your intake up to your new, lower maintenance level.

To set a target weight and pace and see your daily calories, use the calorie goal planner.