Calorie deficit calculator
A calorie deficit is the gap between what your body spends in a day and what you eat. Enter your details, pick a pace, and the calculator returns both your maintenance level and a daily target. For most people a safe range is 10 to 20 percent below maintenance, which is 0.25 to 0.5 kg per week.
Built on the Mifflin-St Jeor equation with the standard activity multipliers. Below you can see where every number comes from and where published research ends and our settings begin.
How the deficit is calculated
First comes resting metabolic rate, what your body spends at complete rest, from the Mifflin-St Jeor equation. That gets multiplied by an activity factor to give maintenance, the level at which weight stays flat. The deficit is subtracted from there: every 0.25 kg per week costs roughly 275 kcal a day.
Activity multipliers are the standard ones: 1.2 for a desk job with no training, 1.375 for light activity, 1.55 for training 3 to 5 times a week, 1.725 for 6 to 7, and 1.9 for hard physical work. Two things here are unusual compared with other calculators. The result never falls below a safety floor of 1,500 kcal for men and 1,200 for women, because past that point what suffers is sleep, hormones and your ability to train rather than fat stores. And active calories from a watch are credited back at half value, because wearables consistently overestimate expenditure.
Why there is no target date
It is tempting to divide a deficit by 7,700 kcal and print a date. Plenty of calculators do, and it is wrong: expenditure falls as body weight falls, so the curve flattens and the promised date keeps sliding. Watching three weeks of weight data and adjusting is more honest than believing a straight line.
Cutting while lifting
If you train with weights, the goal is not just lower weight but lower fat. Three things do that together: a moderate rather than aggressive deficit, protein at around 1.8 g per kg, and holding your working weights in the gym. Bar weights dropping during a cut is the first clear sign the deficit has gone too deep.
Method and sources
Reviewed byAnna Yusupova, fitness coach · Updated:
The equation and the ranges come from published research. APX product settings are named separately so they are not mistaken for science.
The choice of equation, the protein range and the fat share come from published research. The rest are APX product settings: a 275 kcal step per 0.25 kg per week, a safety floor of 1,500 kcal for men and 1,200 for women, and returning only half of your active calories rather than all of them, because wearables systematically overestimate expenditure. Any maintenance number is a population estimate. Two people with the same height and weight burn different amounts, so treat the number as a starting point and check it against two to three weeks of weight data.
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO (1990). A new predictive equation for resting energy expenditure in healthy individuals. The American Journal of Clinical Nutrition, 51(2), 241–247 Used for: the resting metabolic rate equation this calculator is built on
- Morton RW, Murphy KT, McKellar SR et al. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength. British Journal of Sports Medicine, 52(6), 376–384 Used for: the protein range for people who lift, which is where 1.8 g per kg comes from
- National Academies of Sciences (2005). Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids. Institute of Medicine, Macronutrients chapter Used for: the acceptable fat range that the 30% of calories default sits inside
- NIDDK, National Institutes of Health. Body Weight Planner: a dynamic model of body weight change. Laboratory of Biological Modeling Used for: why a target date cannot be found by dividing a deficit by 7,700 kcal
This calculator is an educational estimate, not medical advice. Talk to a doctor before major changes to your training or diet.
Frequently asked questions
How big should a calorie deficit be?
For most people 10 to 20 percent below maintenance works, which is roughly 0.25 to 0.5 kg per week. This calculator moves in steps of 275 kcal per day for every 0.25 kg per week. A steeper deficit loses weight faster in the short run but costs more muscle, recovery and adherence, so the result never drops below 1,500 kcal for men or 1,200 for women.
Should I eat back the calories my watch says I burned?
Your activity multiplier already covers regular training, so normally you should not add anything. For an unusually active day, put the active calories into the optional field and the calculator adds half of them back. Half rather than all, because wearables overestimate expenditure and eating the full number quietly erases the deficit.
How long will it take me to lose the weight?
A target date cannot be predicted from a deficit, which is why this calculator deliberately does not show one. The familiar rule that 7,700 kcal equals one kilogram only describes the beginning: as body weight drops, so does expenditure, and the curve flattens. NIDDK publishes a dynamic model of this, linked in the sources below.
Do I need to recalculate as I lose weight?
Yes. Maintenance scales with body weight, so recalculate every 3 to 4 kilograms, otherwise your deficit slowly turns into maintenance. In practice the better signal is the trend: if weight has not moved for two to three weeks and your food logging is honest, your maintenance has already changed.
Can I lose fat without losing muscle?
Largely yes, given a moderate deficit, enough protein at around 1.8 g per kg of body weight, and resistance training. Without training there is no signal to keep the muscle, which is why cutting without lifting tends to cost more of it.
A deficit holds together with training, not willpower
APX plans your lifting and logs every set, so the weight you lose comes off fat instead of muscle.
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