How to calculate cutting calories: the exact math by bodyweight

Cutting calories are not a special number. They are your maintenance calories, your TDEE, minus a deficit. That is the entire formula. A deficit of 500 calories a day produces roughly 0.45 kg of fat loss per week. A deficit of 750 a day produces roughly 0.7 kg per week. Push much faster than that and the weight you lose stops being mostly fat: muscle goes with it, your training suffers, and the cut collapses within weeks. So the real question is not "how few calories can I eat" but "what is the largest deficit I can run without paying for it in muscle." This guide walks the math step by step, gives you the ceiling rule that answers that question, and works the numbers for five bodyweights so you can see exactly where your own target lands.

The calculation, start to finish

Three steps. You estimate your BMR from your stats, multiply it by an activity factor to get your TDEE, then subtract a deficit. If you already know your TDEE from a tracked weight trend, skip straight to step 3; trend data beats any formula. If you only have a calculator number, this is how it is built, and our breakdown of TDEE vs BMR and maintenance calories covers why these three terms keep getting confused.

Step 1: estimate BMR with Mifflin-St Jeor

Mifflin-St Jeor is the most accurate of the common BMR equations for the general population, which is why nearly every serious calculator uses it. It takes weight in kilograms, height in centimeters, and age:

• Men: BMR = 10 × weight + 6.25 × height − 5 × age + 5
• Women: BMR = 10 × weight + 6.25 × height − 5 × age − 161

The result is what your body burns lying still for 24 hours: organs, brain, breathing, body temperature. It is not a number you ever eat at. It is the input for step 2.

Step 2: multiply by an activity factor to get TDEE

Your TDEE adds everything else on top of BMR: training, walking, standing, fidgeting, digestion. The standard multipliers:

• Sedentary (desk job, little exercise): BMR × 1.2
• Lightly active (1 to 3 sessions a week): BMR × 1.375
• Moderately active (3 to 5 sessions a week): BMR × 1.55
• Very active (6 to 7 hard sessions a week): BMR × 1.725

Most lifters training 4 days a week with an otherwise normal job sit at 1.55, and that is the multiplier every worked example below uses. The most common error in this whole calculation is picking a flattering multiplier: training 3 days a week while sitting the other 13 waking hours is moderate, not very active. When in doubt, pick the lower tier; a slightly conservative TDEE costs you nothing, while an inflated one erases your deficit before you start.

Step 3: subtract the deficit

Fat tissue holds roughly 7,700 calories per kilogram, which is where the weekly rates come from. A 500 calorie daily deficit is 3,500 a week, about 0.45 kg of fat. A 750 daily deficit is about 0.7 kg a week. For most intermediate lifters the sensible range is a 400 to 600 calorie deficit: fast enough to see the trend move every week, small enough to train hard and keep muscle. Larger deficits are defensible only for heavier people, because the ceiling below scales with maintenance, not with ambition.

The 20 percent ceiling rule

Here is the rule that separates a productive cut from a crash: never eat below 80 percent of your maintenance. Whatever your TDEE is, multiply it by 0.8 and treat that as the floor for your intake, which makes 20 percent of maintenance the ceiling for your deficit.

Below that line, three things start happening at once. First, muscle loss accelerates: in a steep deficit your body increasingly pulls from lean tissue, not just fat, and no protein target fully protects you. Second, metabolic adaptation kicks in harder: your body downregulates spontaneous movement and thermogenesis to defend against the shortfall, so the real-world deficit shrinks below what the math says. Third, and most decisive in practice, adherence collapses: hunger and fatigue from a very low intake make the diet unsustainable, and a 1,400 calorie plan you abandon in week 3 loses to a 2,000 calorie plan you run for 12 weeks every single time.

Notice what the rule implies: the deficit scales with the person. A 100 kg man with a 3,200 maintenance has room for a 640 calorie deficit. A 55 kg woman with an 1,850 maintenance has room for about 370. The internet's default "eat 1,200 calories" advice ignores this completely, which is why it works as a crash and fails as a cut.

Worked examples: 5 bodyweights, full math

Each example uses Mifflin-St Jeor, the moderate multiplier of 1.55, and a deficit at or near the 20 percent ceiling, the most aggressive cut that is still defensible. If you would rather cut slower, anything from a 300 calorie deficit up to these numbers is a valid choice; the ceiling is a limit, not a prescription.

70 kg male, 175 cm, 35, moderate activity

• BMR: 10 × 70 + 6.25 × 175 − 5 × 35 + 5 = 1,624
• TDEE: 1,624 × 1.55 = 2,517, call it 2,500 maintenance
• Cut: 2,500 − 500 = 2,000 calories, a 20 percent deficit, roughly 0.45 kg per week

85 kg male, 183 cm, 28, moderate activity

• BMR: 10 × 85 + 6.25 × 183 − 5 × 28 + 5 = 1,859
• TDEE: 1,859 × 1.55 = 2,881, call it 2,900 maintenance
• Cut: 2,900 − 600 = 2,300 calories, right at the ceiling, roughly 0.55 kg per week

100 kg male, 190 cm, 25, moderate activity

• BMR: 10 × 100 + 6.25 × 190 − 5 × 25 + 5 = 2,068
• TDEE: 2,068 × 1.55 = 3,205, call it 3,200 maintenance
• Cut: 3,200 − 650 = 2,550 calories, right at the ceiling, roughly 0.6 kg per week

55 kg female, 160 cm, 40, moderate activity

• BMR: 10 × 55 + 6.25 × 160 − 5 × 40 − 161 = 1,189
• TDEE: 1,189 × 1.55 = 1,843, call it 1,850 maintenance
• Cut: 1,850 − 350 = 1,500 calories, just under the ceiling, roughly 0.3 kg per week

70 kg female, 168 cm, 40, moderate activity

• BMR: 10 × 70 + 6.25 × 168 − 5 × 40 − 161 = 1,389
• TDEE: 1,389 × 1.55 = 2,153, call it 2,150 maintenance
• Cut: 2,150 − 450 = 1,700 calories, right at the ceiling, roughly 0.4 kg per week

Two things to take from the table. The smaller you are, the smaller the defensible deficit, so the 55 kg example loses weight at roughly half the rate of the 100 kg example and that is correct, not a problem to fix. And every one of these numbers is an estimate that only becomes accurate once you check it against your scale trend over two to three weeks, which is where the adjustment rules below come in.

Protein goes up on a cut, not down

The counterintuitive rule of cutting: as calories drop, protein rises. At maintenance, 1.6 to 2.2 g per kg covers muscle growth. In a deficit, bump it to 2.0 to 2.4 g per kg. The deficit itself is a muscle-loss signal, and a higher protein intake is the strongest dietary counter-signal you have: it preserves lean mass, blunts hunger more than carbs or fat per calorie, and costs more energy to digest.

For the 70 kg male above, that is 140 to 168 g of protein a day inside a 2,000 calorie budget; for the 55 kg female, 110 to 132 g inside 1,500. Protein gets set first, in grams, and carbs and fat split whatever calories remain. If your goal is closer to holding weight while swapping fat for muscle, the math changes; the body recomposition guide covers that case, and for many newer lifters it is the better play than a dedicated cut.

When the scale stalls: adjust one lever, not two

Every formula number is a starting estimate, and your maintenance also genuinely drops as you get lighter, so stalls are expected on any cut longer than a few weeks. The rule: if your weekly average weight has not moved for 2 consecutive weeks, make one adjustment. Either drop intake by 100 to 150 calories, or add roughly 1,500 daily steps. Do not do both. Stacking both at once is how a controlled 20 percent cut quietly turns into a 30 percent crash, and it leaves you with no next move for the stall after this one.

Judge stalls on the weekly average, never on a single weigh-in: day-to-day weight swings on water, sodium, and glycogen by more than most weekly fat loss. And if you are tempted to solve a stall with more cardio instead, the comparison in HIIT vs steady-state cardio for fat loss explains why extra steps are usually the cheaper lever: they add expenditure without eating into recovery the way more hard conditioning does.

Refeeds: for cuts running past 8 weeks

If your cut will run longer than 8 weeks, schedule 1 to 2 refeed days every 7 to 10 days: days where you eat at maintenance, with the extra calories going almost entirely to carbs while protein stays put and fat stays low. A refeed is not a cheat day. It is a planned maintenance day that refills muscle glycogen so training quality holds, gives leptin and your perceived energy a periodic lift, and gives you a recurring psychological release valve that makes a 12 to 16 week cut survivable. The cost is trivial: one maintenance day in ten slows the overall rate by about 10 percent, and most people more than recover that through better training and better adherence on the deficit days.

Refeeds also preview the exit. A cut is not finished until you return to maintenance without rebounding, and that return is its own protocol: a structured ramp back up rather than a celebratory jump. When you are within sight of your goal weight, read reverse dieting after a cut before you get there, because the week after a cut ends is where most of the regain happens.

Frequently asked questions

How many calories should I eat to lose weight?

Your TDEE minus 400 to 600 calories for most people, and never less than 80 percent of your TDEE. Calculate BMR with Mifflin-St Jeor, multiply by your activity factor (1.55 for someone training 3 to 5 days a week), then subtract the deficit. A 70 kg moderately active man lands around 2,000; a 55 kg moderately active woman around 1,500. Then verify against your scale trend for two to three weeks, because every formula is an estimate.

Is a 500 calorie deficit too much?

For most people training regularly, no. A 500 calorie deficit produces roughly 0.45 kg of fat loss per week and sits at or under the 20 percent ceiling for anyone whose maintenance is 2,500 or higher. It becomes too much for smaller or lighter people: at an 1,850 maintenance, 500 calories is a 27 percent deficit, past the line where muscle loss and adherence problems start. Scale the deficit to your maintenance, not to a default number.

Why am I not losing weight in a calorie deficit?

Usually one of three reasons. Your TDEE estimate was high, often from picking a flattering activity multiplier, so your "deficit" is closer to maintenance. Your intake is drifting above target through untracked oils, sauces, and weekend meals. Or you are judging by single weigh-ins instead of weekly averages and a real loss is hidden under water-weight noise. Track for 2 full weeks; if the weekly average truly has not moved, drop 100 to 150 calories or add 1,500 daily steps, not both.

Should I eat back exercise calories on a cut?

No. The activity multiplier in your TDEE already accounts for your training, so eating back exercise calories counts the same workout twice and erases your deficit. Fitness watches also overestimate session burn, often badly. The clean approach: set your cutting target from TDEE, keep it the same on training and rest days, and let your weekly weight trend tell you whether the deficit is real.

How fast should I lose weight without losing muscle?

Around 0.5 to 1 percent of bodyweight per week, which for most people maps to a 400 to 750 calorie deficit. Inside that range, with protein at 2.0 to 2.4 g per kg and continued lifting, losses are mostly fat. Faster than 1 percent a week reliably costs muscle, regardless of protein, because the energy shortfall is too large for fat stores to cover alone. Patient cuts keep the muscle that makes the end result worth looking at.

The whole calculation fits on an index card: Mifflin-St Jeor for BMR, times your honest activity multiplier for TDEE, minus a deficit no bigger than 20 percent of maintenance. Protein up to 2.0 to 2.4 g per kg, one adjustment lever per stall, refeeds past week 8, and a structured return to maintenance when you are done. If you want the numbers maintained for you instead of by you, the TDEE & Macro Planner recalculates your targets as your weight drops, and TDEE vs BMR and maintenance calories is the right primer if any of the three numbers still feel interchangeable.