Calorie deficit: how to calculate it to lose weight
In short
- A calorie deficit means eating fewer calories than you burn. No diet works without one.
- A safe pace is 0.5-1% of body weight a week, usually a deficit of about 300-550 kcal a day.
- Calculate maintenance with the Mifflin-St Jeor equation, multiply by activity, then subtract the deficit.
- Weight loss slows over time because a lighter body burns less, so recalculate every few weeks.
A calorie deficit means eating fewer calories than your body burns in a day. The gap comes from stored energy, mostly body fat. For weight loss, a deficit of 15-25% below maintenance is enough, which is about 300-600 kcal a day for most people. The quickest way to get your number is the calorie deficit calculator.
What is a calorie deficit?
Your body burns energy on three things: keeping organs running at rest, movement and digesting food. Together this is your maintenance calories, also called TDEE (total daily energy expenditure). Eat exactly that and your weight stays the same. Eat less and you are in a deficit.
The mix of foods matters less than the deficit itself. In a study by Sacks and colleagues (2009), 811 adults spent two years on diets with different amounts of fat, protein and carbs. Weight loss was similar on all of them. Keto, intermittent fasting and clean eating all work the same way: they help you eat less.
How to calculate a calorie deficit
- Basal metabolic rate. The Mifflin-St Jeor equation (1990): for men 10 × weight in kg + 6.25 × height in cm − 5 × age + 5. For women, subtract 161 at the end instead of adding 5.
- Maintenance (TDEE). Multiply by an activity factor: about 1.4 for a desk job, 1.5 if you walk a lot, 1.65-1.8 for an active job.
- Deficit. Subtract 275, 550 or 825 kcal for a loss of about 0.5, 1 or 1.5 lb (0.25, 0.5 or 0.75 kg) a week.
Example: a 30-year-old woman, 5 ft 6 in (168 cm), 154 lb (70 kg), desk job. Her BMR is 1,439 kcal and maintenance about 2,010 kcal. At a moderate pace her daily target is about 1,460 kcal. The TDEE calculator does this math for you.
How big a deficit is safe?
A very large deficit shows fast numbers on the scale at first, but much of it is water and muscle. Hunger rises, energy for training drops and slips become more likely.
| Pace | Daily deficit | Best for |
|---|---|---|
| 0.5 lb (0.25 kg) a week | about 275 kcal | close to goal, keeping strength |
| 1 lb (0.5 kg) a week | about 550 kcal | most people |
| 1.5 lb (0.75 kg) a week | about 825 kcal | a lot to lose at 175 lb (80 kg) or more, for a limited time |
A simple safety rule: do not lose more than 1% of body weight a week, about 1.5 lb (0.7 kg) at 154 lb (70 kg), and do not go below about 1,200 kcal for women or 1,500 kcal for men without a doctor.
Why weight loss slows down
The old rule of 3,500 kcal per pound of fat only holds at the start. Hall and colleagues (2011) showed with a mathematical model that energy needs fall as you lose weight: a lighter body costs less to move. The same deficit gives less loss after a couple of months.
The fix is not to cut harder, but to recalculate maintenance for your new weight every 2-3 weeks. The other common reason for a plateau is unlogged food: cooking oil, sauces and snacks on the go.
How to keep muscle in a deficit
Protein is the main tool. A systematic review by Helms and colleagues (2014) in lean, trained people found that muscle was best preserved at 2.3-3.1 g of protein per kg of lean body mass. For most people that is about 1.8-2.2 g per kg of body weight. Read more in how much protein do I need a day.
The second tool is strength training two or three times a week. It tells your body the muscle is needed, so the deficit takes mostly fat. A full body routine or bodyweight exercises at home both work.
Bottom line
Start with a moderate deficit of 300-550 kcal, keep protein high and weigh yourself weekly. Recalculate your maintenance every 2-3 weeks and a plateau will not catch you by surprise.
Tonus calculates your calorie target with the same formula as the calculators on this site and updates it when you log a new weight. You can log food with a photo of your plate, by voice or by text, so tracking does not need a scale for every meal.
Frequently asked questions
How big should my calorie deficit be?
Usually 15-25% below maintenance, which is 300-600 kcal a day for most adults. That gives about 0.5-1.5 lb (0.25-0.75 kg) of loss a week without constant hunger.
Is 1,200 calories a day a safe deficit?
1,200 kcal is roughly the lowest intake for women and 1,500 kcal for men without medical supervision. Many people do better on more food and a slower pace.
Why am I not losing weight in a calorie deficit?
Most often calories are underestimated: cooking oil, sauces and snacks go unlogged. Weight also swings 2-4 lb (1-2 kg) with water, so judge by the weekly average, not one weigh-in.
Sources
- Mifflin M. D. et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr, 1990 doi.org/10.1093/ajcn/51.2.241
- Hall K. D. et al. Quantification of the effect of energy imbalance on bodyweight. Lancet, 2011 doi.org/10.1016/S0140-6736(11)60812-X
- Sacks F. M. et al. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. N Engl J Med, 2009 doi.org/10.1056/NEJMoa0804748
- Helms E. R. et al. A systematic review of dietary protein during caloric restriction in resistance trained lean athletes. Int J Sport Nutr Exerc Metab, 2014 doi.org/10.1123/ijsnem.2013-0054
This article is for general information and does not replace medical advice.
