Calorie Deficit: What It Is and How to Calculate Yours
By the DietX team · Updated · 7 min read
A calorie deficit means eating fewer calories than your body burns, so it draws on stored energy to cover the gap. To calculate yours, work out your maintenance calories and subtract about 300 to 500 kcal a day. If you maintain on 1,920 kcal, that gives you a target of 1,420 to 1,620 kcal.
Below you'll find the math, why a bigger cut isn't a better one, and how to tell whether your deficit is working.
What is a calorie deficit?
Your body spends energy all day, at rest and on the move. The total is your maintenance calories: roughly what you could eat each day without your weight changing. Eat less than that and you're in a deficit. Eat more and you're in a surplus.
A deficit is an average over days and weeks. One big dinner doesn't cancel it, and one careful day doesn't create it.
It can come from eating less, moving more, or both. Just don't count on exercise alone: weight loss from exercise is usually less than expected, because the body compensates. Moving is still well worth doing for your health, and we come back to it below.
How to calculate a calorie deficit
- Find your maintenance calories. Our guide to how many calories you need a day takes you through the formula in a couple of minutes.
- Subtract 300 to 500 kcal. Start at the lower end if you're smaller or not very active.
- Check the result. If it lands below about 1,200 kcal, don't follow it. Talk to a doctor or dietitian instead.
Here is how that works for the two people in that guide:
| Woman, 35, 165 cm, 70 kg, light activity | Man, 35, 180 cm, 85 kg, moderate activity | |
|---|---|---|
| Maintenance | about 1,920 kcal | about 2,800 kcal |
| 300 kcal deficit | 1,620 kcal | 2,500 kcal |
| 500 kcal deficit | 1,420 kcal | 2,300 kcal |
| 500 kcal as a share of maintenance | 26% | 18% |
The last row is the one to notice. The same 500 kcal is a much bigger cut for her than for him, which is why a smaller, less active person may do better near 300 kcal.
If you want to know what sits behind the maintenance number, read BMR, TDEE and maintenance calories explained.
How big should your calorie deficit be?
The NHS suggests aiming to lose 0.5 to 1 kg (1 to 2 lb) a week, and the CDC notes that people who lose weight gradually and steadily at about that pace are more likely to keep it off.
To turn a deficit into a weekly pace, people often use an old shortcut: 3,500 kcal equals about 1 lb of body weight. So 500 kcal a day × 7 days = 3,500 kcal a week, or about 1 lb (0.45 kg). A 300 kcal deficit works out to about 0.6 lb (0.27 kg).
Treat that as a first guess. Research on energy balance shows the shortcut overpromises over the long term, because body weight responds slowly and your needs fall as you get lighter. Our article on how long it takes to lose weight has realistic timelines.
Why not a bigger deficit?
By that same shortcut, 2 lb a week takes about 1,000 kcal a day. Here is what that does to the two people above:
- The woman would land at 920 kcal, well under the 1,200 kcal mark. Please don't do this.
- The man would land at 1,800 kcal. That's possible on paper, but it's a cut of 36% of what he burns, which is a lot to keep up for months.
Big cuts are hard to sustain, can leave you short of nutrients and can be harmful. A smaller deficit you can live with for months beats a harsh one you drop after two weeks.
Protein and strength work: keeping muscle while you lose fat
When you lose weight, some of what goes is lean mass rather than fat. Two habits can help tilt that toward fat.
Eat enough protein. A review of higher-protein diets found more weight and fat loss and more lean mass kept in shorter controlled trials, plus a modest effect on fullness, though long-term results depend on sticking with the diet. For people who exercise, a position stand from the International Society of Sports Nutrition says 1.4 to 2.0 g per kg of body weight a day is enough for most. At 70 kg, that's 98 to 140 g. Our guide to how much protein you need per day has a table by body weight.
Do some strength work. The WHO and the NHS advise adults to do at least 150 minutes of moderate activity a week, plus strength work on at least 2 days. Muscle you keep using is muscle you have a better chance of keeping.
How to know your calorie deficit is working
The scale is the simplest check, as long as you read it the right way. Daily weight jumps around for reasons that have nothing to do with fat, so don't judge from single days. Weigh yourself a few mornings a week and compare weekly averages, because weight also tends to rise on weekends and fall during the week. A review of self-weighing linked the habit with more weight loss and not with negative psychological outcomes. If the scale upsets you all the same, it's fine to stop.
After two to three weeks at your target, use this as a guide:
| Your weekly average | What it suggests | What to do |
|---|---|---|
| Falling gradually | The deficit is working | Keep going |
| Falling more than about 1 kg a week after the first weeks | The deficit may be too big | Eat 100 to 200 kcal more |
| Flat | The deficit may be smaller than you think | Check your logging first, then try 100 to 200 kcal less, staying above 1,200 kcal |
| Rising | You may be above maintenance | Check your logging and your weekends |
If you're constantly hungry, worn out or thinking about food all day, take that as a sign too, and eat more. And if the trend has stalled, go through our checklist for being in a deficit but not losing weight before you cut anything.
Making a deficit easier to keep
Start with the changes you'll barely notice. The NHS suggests swapping sugary drinks for water, and that alone can cover a good part of a small deficit if you drink them often. A simple meal plan built around your target also helps on busy days, when decisions are what wear you down.
Then make sure the numbers you're steering by are real. In a small study of 10 adults who described themselves as "diet-resistant", people under-reported their food by 47%. That's a small, specific group, so don't read it as typical, but the direction is common enough that we wrote up the usual calorie tracking mistakes.
Logging takes time, too. In one study of 142 adults, it took 23.2 minutes a day in the first month and 14.6 by the sixth. DietX sets a daily target from your age, height, weight, activity level and goal, then lets you log a meal with a photo, a typed description, your voice or a barcode, and edit any item before you save it. Its estimates can vary, so glance over them. It's free to download with a free trial, and Premium is a subscription.
Frequently asked questions
What is a good calorie deficit to lose weight?
A common starting point is 300 to 500 kcal a day below your maintenance calories. Smaller, less active people may do better near 300 kcal, because the same cut is a bigger share of what they burn. If the result is below about 1,200 kcal, talk to a doctor or dietitian.
How do I calculate my calorie deficit?
Estimate your maintenance calories with a formula such as Mifflin-St Jeor and an activity multiplier, then subtract your chosen deficit. If you maintain on about 2,000 kcal, a 400 kcal deficit means eating about 1,600 kcal a day.
Is a 1,000 calorie deficit safe?
For many people it is too much. A woman who maintains on about 1,920 kcal would land at 920 kcal, well below the roughly 1,200 kcal level where you should get medical advice. Very low intakes are hard to sustain and can be harmful.
How long does it take to see results from a calorie deficit?
Give it two to three weeks before you judge it, and compare weekly average weights rather than single days. Water can hide real progress in the short term, and results vary from person to person.
Can I be in a calorie deficit without counting calories?
Yes. Smaller portions, fewer sugary drinks and more movement can all create a deficit without a log. Counting makes it easier to measure, but it isn’t for everyone. If tracking food makes you anxious, skip it.
Sources
- Riou et al. (2015), Nutrients: Predictors of energy compensation during exercise
- NHS: Tips to help you lose weight
- CDC: Steps for losing weight
- Hall et al. (2011), Lancet: Quantification of the effect of energy imbalance on bodyweight
- NHS: Eating disorders
- Leidy et al. (2015), Am J Clin Nutr: The role of protein in weight loss and maintenance
- Jäger et al. (2017), J Int Soc Sports Nutr: ISSN position stand on protein and exercise
- WHO: Physical activity
- NHS: Physical activity guidelines for adults
- Orsama et al. (2014), Obes Facts: Weight rhythms across the week
- Zheng et al. (2015), Obesity: Self-weighing in weight management, a systematic review
- Lichtman et al. (1992), N Engl J Med: Self-reported and actual caloric intake and exercise
- Harvey et al. (2019), Obesity: Log Often, Lose More
General information, not medical advice. Talk to a doctor or dietitian before changing your diet, especially if you are pregnant, under 18 or have a health condition. If tracking food makes you anxious or you have a history of disordered eating, please skip calorie counting and ask a professional for support.
