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nutrition · weight loss

How to calculate a calorie deficit.

A calorie deficit just means eating fewer calories than your body uses, so it draws on stored energy and you lose weight. Calculating your own is four short steps: estimate what you burn, choose how big a gap to run, subtract to get a daily target, then let a couple of weeks of real data correct the estimate. Here is the whole method, with the formulas and a worked example.

By Markus Evers · Updated August 2026

the short answer

Estimate your maintenance calories (your TDEE) with the Mifflin-St Jeor equation, then subtract a deficit. A daily deficit of about 500 calories tends to produce roughly half a kilo (about one pound) of loss a week, so if you maintain on 2,740 calories, your target becomes about 2,240. Hold it for two to three weeks and adjust from the scale trend, because the formula is only a starting estimate. A calorie deficit calculator does the arithmetic in seconds.

This article is general information, not medical or dietetic advice. Individual needs vary, so anyone with a health condition, a history of disordered eating, who is pregnant or breastfeeding, or considering a very low intake should speak with a doctor or registered dietitian before setting a deficit.

the idea in one minute

What a calorie deficit actually is.

Every day your body spends energy: keeping you alive at rest, digesting food, and moving around. Add those up and you get your total daily energy expenditure, or TDEE, which is the number of calories that would keep your weight steady. Eat that amount and you maintain. Eat fewer than that and you are in a calorie deficit, so your body makes up the difference from stored energy, and over time you lose weight.

That is the entire principle, and calculating a deficit is just putting numbers on it: work out roughly what you burn, decide how big a gap to run, and set the intake that creates it. The four steps below do exactly that. None of them needs anything fancier than the formula, a calculator, and a scale.

the method

How to calculate your calorie deficit in four steps.

Do them in order. The first step is the only one with real arithmetic; the rest is a single subtraction and then a few weeks of paying attention.

01

Estimate your maintenance calories (TDEE).

Start with your basal metabolic rate (BMR), the energy you burn at complete rest. The most reliable everyday formula is the Mifflin-St Jeor equation, which uses your weight, height, age, and sex:

Men: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age(years) + 5

Women: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age(years) - 161

Then multiply your BMR by an activity factor to account for movement and training. That product is your TDEE, your maintenance calories. Pick the factor that honestly matches a normal week, and when you are unsure, choose the lower one:

Activity level Factor Roughly who
Sedentary 1.2 Desk job, little or no deliberate exercise.
Lightly active 1.375 Light exercise or sport one to three days a week.
Moderately active 1.55 Moderate exercise three to five days a week.
Very active 1.725 Hard exercise six or seven days a week.
Extra active 1.9 Hard daily training, or a physical job on top of training.

The formula gives a population average, not a personal measurement, so treat the result as a well-informed starting point. Step four is where you correct it for the body actually in front of the scale. If you would rather not do this by hand, a TDEE calculator or a maintenance calorie calculator runs the same equation for you.

02

Choose your deficit size.

Now decide how big a gap to run below maintenance. The classic starting point is about 500 calories a day. That works out to a 3,500 calorie deficit across the week, and because a kilo of body fat holds roughly 7,700 calories, that predicts close to half a kilo (about one pound) of loss a week. It is a rule of thumb, not a law, but it is a sensible place to begin.

A better way to size it is as a percentage of your bodyweight: aiming to lose about 0.5 to 1 percent of your weight per week keeps the deficit sustainable and protects muscle. A lighter person should lean toward a smaller deficit (say 250 to 350 calories), while a heavier person can usually handle a larger one. Faster is not better here. A moderate deficit you can hold for months beats an aggressive one you quit in a fortnight.

03

Set your daily calorie target.

This step is a single subtraction: your target equals your maintenance calories minus your deficit. If your TDEE is 2,740 and you choose a 500 calorie deficit, your daily target is 2,240 calories. That is the number to eat around each day. Do not chase it to the exact calorie; a daily average across the week that lands near your target is what actually drives the result, so a slightly higher day balanced by a lower one is completely fine.

04

Calibrate against your real weight trend.

Here is the step the calculators cannot do for you, and the one that makes the whole thing accurate. Your calculated maintenance is an estimate built from population averages, so your real maintenance might be a couple of hundred calories either side of it. The way to find the truth is to eat at your target for two to three weeks, weigh yourself regularly under the same conditions, and read the trend rather than any single morning.

If the trend shows you losing at roughly the rate you planned, the estimate was good, so keep going. If you are losing slower than about half a percent of bodyweight a week, trim another 100 to 200 calories or add some activity, and since a daily walking target is the simplest lever there, it helps to know how many steps a day you actually need. If you are dropping too fast or feeling drained, ease the target back up. From then on the scale, not the formula, is your instrument, and it keeps you honest as your maintenance drifts down with your bodyweight.

worked example

Start to finish: an 80 kg, 178 cm, 30-year-old man, moderately active.

  1. BMR: 10 x 80 + 6.25 x 178 - 5 x 30 + 5 = 800 + 1,112.5 - 150 + 5 = about 1,768 calories.
  2. TDEE: 1,768 x 1.55 (moderately active) = about 2,740 calories, his maintenance.
  3. Deficit: he chooses 500 calories a day, which sits inside the 0.5 to 1 percent per week band for his weight.
  4. Target: 2,740 - 500 = 2,240 calories a day.
  5. Expected rate: 500 x 7 = 3,500 calories a week, so roughly 0.45 kg (about a pound) of loss a week, then confirmed and adjusted from his real trend.
step one, in detail

Harris-Benedict, Mifflin-St Jeor or Katch-McArdle: which equation to use.

Step one estimates the calories your body burns at rest. Three equations dominate, they disagree by a few hundred calories on the same person, and which one is right for you depends on a single question: do you know your body fat percentage?

Equation What it needs When it wins
Harris-Benedict (revised 1984)Weight, height, age, sexRarely. It was fitted on an older, more active population and tends to read high today.
Mifflin-St Jeor (1990)Weight, height, age, sexThe default. Validation work ranks it the most accurate when body composition is unknown.
Katch-McArdleLean body massLean, muscular people who have a real body fat measurement, where total weight misleads.

Harris-Benedict is the oldest of the three and was the clinical standard for decades. Its revision still circulates in older calculators, but because it was derived from a population that moved more than most people do now, it usually returns a higher BMR than the person actually has, which is the wrong direction for a weight-loss target.

Mifflin-St Jeor was fitted on newer data and has repeatedly come out ahead in validation studies when nothing is known about body composition, which is why it is the equation behind the calorie deficit calculator and the TDEE calculator. For most people reading this, it is simply the right default and there is no decision to make.

Katch-McArdle ignores total weight and works from lean mass instead: BMR = 370 + 21.6 x lean mass in kg. That makes it the better estimate for someone lean and muscular, whose weight overstates how much tissue is metabolically demanding, and it needs a real body fat number to run. Measure that with the body fat calculator and convert it with the lean body mass calculator. If Katch-McArdle and Mifflin-St Jeor disagree by more than about 150 calories, do not agonise over which is right: run either target for two to three weeks and let your real weight trend settle it.

skip the arithmetic

Free calculators that do the maths for you.

The steps above are worth understanding, but you do not have to run them by hand every time. These three free calculators use the same Mifflin-St Jeor equation and activity factors, so you can get to your number in seconds and spend your attention on the part that matters, the weekly trend.

calculator

Calorie deficit calculator.

Enter your details and a rate of loss, and it returns your maintenance and your daily deficit target in one go.

Open the calculator

calculator

TDEE calculator.

Just want step one? This returns your total daily energy expenditure so you can set any deficit yourself.

Open the calculator

calculator

Maintenance calorie calculator.

The calories that hold your weight steady, which is the baseline every deficit is measured down from.

Open the calculator
where the number goes wrong

Common mistakes that break the maths.

When a carefully calculated deficit does not deliver, it is almost never because the arithmetic was wrong. It is one of these four assumptions quietly being off.

Picking an activity factor that is too high

This is the single most common reason the maths says one thing and the scale says another. Most people who train a few times a week are moderately active (1.55), not very active (1.725). Rating yourself one level up can inflate your maintenance estimate by two to three hundred calories, which quietly erases the deficit you thought you set. When in doubt, choose the lower factor and let two to three weeks of real weight data correct it upward if needed.

Setting a deficit that is too aggressive

A bigger deficit is not a faster win. Very large deficits are harder to stick to, leave you hungry and low on energy, and put more of your hard-won muscle at risk alongside the fat, especially if protein and resistance training are not in place. For most people, losing about 0.5 to 1 percent of bodyweight a week is the sustainable band. Slower and consistent beats fast and abandoned by week three.

Never recalculating as the weight comes off

Your maintenance calories are tied to your bodyweight, so a lighter you burns fewer calories at rest and in motion. The deficit that produced steady loss at the start will slowly shrink to nothing as you get lighter, which is why almost everyone stalls eventually. Recheck your maintenance estimate every few kilograms, or simply keep adjusting from the scale trend, so the target keeps pace with the smaller body doing the work.

Underestimating what you actually eat

Calculators assume you know your intake, but unlogged bites, generous eyeballed portions, cooking oils, drinks, and a looser weekend are easy to miss and add up fast. If the target looks right on paper but nothing moves, honest tracking for a week or two is usually more revealing than any formula. The number you calculate only becomes a real deficit if the food actually matches it.

for coaches

How coaches run this calculation with clients.

The arithmetic above is the easy half. What separates a coach's target from a calculator's output is what happens in the three weeks after it: the first number is a hypothesis, and the client's own weight trend is the only thing that confirms or corrects it. Coaches set the target before week one so the client has something specific to act on, then treat the first fortnight of check-in data as the real measurement and move the target to match.

Two judgment calls do most of the work. The first is how aggressive to go: most coaches hold weekly loss between roughly 0.5 and 1 percent of body weight, because faster than that costs muscle, sleep and adherence long before it costs fat. The second is where to floor the target, since the same 500 calorie deficit that is comfortable for a 100 kg client puts a 52 kg client under 1,200 calories. Both are worked through in how to set a client's calorie target.

From there the target becomes macros, and the deficit becomes a phase with an end date rather than an open-ended diet. See how to calculate TDEE and macros for clients for the split, and how to do nutrition coaching online for the wider playbook. A calculator gives one person one number; a coaching platform sets a calorie and macro target for every client once and tracks it against weekly check-ins automatically.

common questions

Frequently asked questions about calculating a calorie deficit.

How do I calculate my calorie deficit?

Work it in four steps. First, estimate your maintenance calories (TDEE) by finding your BMR with the Mifflin-St Jeor equation and multiplying by an activity factor. Second, choose a deficit size, with about 500 calories a day being a common starting point for roughly half a kilo of loss a week. Third, subtract the deficit from your maintenance to get your daily calorie target. Fourth, hold that target for two to three weeks and adjust from your actual weight trend, because the formula is only a starting estimate. A calorie deficit calculator does the arithmetic for you in seconds.

What should my calorie deficit be?

A deficit that loses about 0.5 to 1 percent of your bodyweight per week is the sustainable range for most people. In calorie terms that is often a 300 to 600 calorie daily deficit, with 500 a day a reasonable default that tends to produce close to half a kilo of loss a week. Leaner or lighter people usually need a smaller deficit, and heavier people can often sustain a larger one, so scaling it to your bodyweight is more reliable than copying a fixed number.

Is a 500 calorie deficit right for everyone?

No. The 500 calorie figure is a useful starting point, not a universal rule. It comes from the rough idea that a kilo of fat holds around 7,700 calories, so a 3,500 calorie weekly deficit predicts about half a kilo of loss. But 500 calories is a much larger share of a small persons maintenance than a large persons, so the same number can be too aggressive for one person and too mild for another. Setting the deficit as a percentage of bodyweight, then adjusting from real results, fits the individual far better.

Why am I not losing weight in a calorie deficit?

Usually one of three honest reasons, and none of them mean the maths is broken. First, the deficit may not be as big as you think: an overestimated activity factor or under-recorded intake can wipe it out, so your calculated deficit is not a real one. Second, day-to-day water shifts from sodium, stress, hormones, or new training can hide fat loss for a week or more, which is why a single weigh-in misleads. Third, you may not have given it long enough; weight needs a two to three week trend to read through the noise. If loss stays stalled despite genuine, consistent adherence, that is a good point to talk to a doctor or registered dietitian.

When should I adjust my calorie target?

Wait for a trend, not a single reading. Give any target two to three weeks so daily fluctuations average out, then compare your weekly weight change against your goal. If you are losing slower than about 0.5 percent of bodyweight a week, drop your intake by roughly 100 to 200 calories or add a little activity. If you are losing faster than a percent a week or feeling wiped out, ease the deficit back up. And recheck your maintenance estimate every few kilograms, since it falls as you get lighter.

Do I need to count calories to be in a deficit?

Not necessarily, but you do need feedback. Tracking calories for a while is the most direct way to know your intake matches your target, and it teaches you portion sizes fast. Once you have that reference, many people maintain a deficit through consistent habits and the weekly scale trend without weighing everything forever. The non-negotiable part is not the app you use; it is watching the trend and adjusting when it stalls.

This article is general information, not medical or dietetic advice. A calorie target is a starting estimate to refine from your own results, not a prescription. Anyone with a health condition, a history of disordered eating, who is pregnant or breastfeeding, or considering a very low intake should work with a doctor or registered dietitian.

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