How to work out your calories and macros, step by step

One app tells you 1,480 calories. A calculator on another site says 1,900. Someone at the gym tells you to eat 2,000 and stop overthinking it. Those three numbers cannot all be right, and there is a decent chance none of them is.

The reason is simple: every formula is an average built from other people's bodies. It gives you a starting point, not an answer. The real number comes from holding that starting point for two or three weeks and reading what the scale did. This guide covers both halves — getting the first number in five minutes, and correcting it afterwards so it fits you.

Decide the goal before you touch the maths

There is no correct calorie number without a goal. The same person in the same week can have three different valid targets depending on what they are trying to do.

• Fat loss: lose fat, keep muscle. Pace of 0.5–1% of body weight per week.
• Maintenance: weight stays inside a 1–1.5 kg band each month, strength holds or climbs.
• Gaining: +0.25–0.5% of body weight per week, slower the longer you have trained.

If you want both at once, pick one and give it 12 to 16 weeks. The arithmetic cannot serve two opposite directions.

Step 1: work out your basal metabolic rate

Your BMR is what your body burns doing nothing — breathing, running organs, holding temperature. For most people who are not doing manual labour, it is 60–70% of the daily total.

The most widely used estimate is the Mifflin-St Jeor equation. You need weight in kilograms, height in centimetres and age.

• Men: (10 × kg) + (6.25 × cm) − (5 × age) + 5
• Women: (10 × kg) + (6.25 × cm) − (5 × age) − 161

That result is an estimate, not a measurement. Two people with identical numbers on paper can differ by 200 calories or more in real burn. You are not chasing a perfect figure, just one good enough to start testing.

Step 2: multiply by an activity factor — and be stingy

Now multiply your BMR by a factor covering movement, training and digestion. This is where most people go wrong, and almost always upwards.

• 1.2 — desk job, no training, little walking
• 1.375 — training 2–3 times a week, or a fair bit of walking
• 1.55 — training 4–5 times a week
• 1.725 — training 6 times a week, or a physical job
• 1.9 — two sessions a day, or heavy manual work

An hour in the gym three times a week does not make you an active person if the rest of the day is a chair and a car. What genuinely moves your burn is the step count across the whole day, and the gap between 4,000 and 10,000 steps is measured in hundreds of calories — the piece on walking and what step count does to your balance goes through the numbers. When you are torn between two factors, take the lower one.

Step 3: add or subtract for the goal

You now have an estimate of daily burn. Shift it.

For fat loss, subtract 300–500 calories. The rough rule is that a kilo of fat is around 7,700 calories, so a 400-calorie daily deficit should give roughly 0.35 kg a week. In practice it is less, because the body quietly moves around less and holds onto water. Deficits above 750 calories only make sense short term and mostly for people carrying more fat; in leaner people they eat into muscle and sleep. The full arithmetic for different body weights sits in the article on the calorie deficit.

For gaining, add 200–350 calories. More than that does not build muscle faster, it just comes along for the ride.

Step 4: set protein first

Protein is the one macro where getting the number wrong has an obvious price — muscle lost in a deficit, slower progress in a surplus.

1.6–2.2 g per kilogram of body weight covers essentially everyone lifting weights. In a deficit, sit in the upper half of that range, around 2.0–2.2 g/kg. If you are carrying a lot of fat, base it on your target weight rather than your current one, or the number comes out unrealistically high.

Protein is 4 calories a gram, so 120 g is 480 calories already committed from your daily budget.

Step 5: put fat at the safe floor, not below it

Fat carries 9 calories a gram and your body needs it for hormones and vitamin absorption. A realistic range is 0.7–1.0 g per kilogram, and there is no reason to drop below 20% of total calories even on an aggressive diet.

If you like richer food, take the top of the range and pull carbs down. If you train hard and often, take the bottom and leave more carbs for training. Neither is better on its own.

Step 6: whatever is left becomes carbs

Add up the calories from protein and fat, subtract that from your daily target, and divide the remainder by 4. Those are your carb grams.

Carbs go last because they are the most flexible lever, not because they matter least. They are what puts force behind your last few sets.

A full worked example

Woman, 32, 68 kg, 168 cm, training three times a week, desk job. Goal: fat loss.

1. BMR: (10 × 68) + (6.25 × 168) − (5 × 32) − 161 = 680 + 1,050 − 160 − 161 = 1,409 kcal
2. Factor 1.375: 1,409 × 1.375 = 1,937 kcal of daily burn
3. Deficit of 400: target is 1,540 kcal
4. Protein at 1.8 g/kg: 122 g, rounded to 120 g = 480 kcal
5. Fat at 0.8 g/kg: 54 g, rounded to 55 g = 495 kcal
6. Remainder: 1,540 − 480 − 495 = 565 kcal ÷ 4 = 140 g of carbs

Her starting point is 1,540 kcal, 120 g protein, 55 g fat, 140 g carbs. Not because it is correct, but because it is something specific enough to test.

Step 7: three weeks of testing, then adjust

Weigh yourself every morning, after the loo and before breakfast, and work with the weekly average. A single day tells you nothing — water, salt and gut contents shift the scale by a kilo and a half without any change in fat. If you have just changed how much salt or fluid you take in, that first jump is almost certainly water; the piece on salt, potassium and electrolytes from ordinary food explains why.

After three weeks, compare the average of week one with week three:

• Losing at the planned pace — change nothing.
• Nothing moved and you tracked honestly — cut 150–200 calories, or add 2,000 steps a day.
• Losing faster than 1% a week — add 150 calories back, usually as carbs.

Change one thing at a time and give it at least two weeks. Adjusting every few days turns a plan back into guesswork.

Common mistakes

An inflated activity factor. The single most common reason the numbers do not work. Drop one level before you conclude you have a slow metabolism.

Eyeballing oil, spreads and nuts. A tablespoon of oil is about 120 calories, a handful of almonds around 180. Three loose guesses a day swallow the whole deficit.

Five tight days, two blank ones. A weekend running 1,000 calories over per day erases the week's work. The weekly total is what decides.

Skipping fibre while chasing decimals. Hit your macros perfectly on 8 g of fibre a day and you will be hungry and sleeping badly. Aim for 25–35 g.

Never recalculating. Once you are 8 kg lighter, your burn has changed. Redo the maths every 5–6 kg, and think about the phase after the diet in advance — the article on keeping the weight off over 12 months lays out that plan.

When to see a doctor

Speak to a doctor before setting your own deficit if you have diabetes, thyroid, kidney or liver disease, if you are pregnant or breastfeeding, if you take medication timed around meals, or if you have a history of disordered eating.

The same applies if weight is dropping quickly without you intending it, if periods have been absent for two months or more, or if you have persistent dizziness and exhaustion that does not lift even after eating normally.

Common questions

Do I have to weigh food forever?

No. Weigh for three or four weeks so you learn what 100 g of rice and 150 g of chicken actually look like. After that most people can estimate within 10–15%, which is plenty for maintenance.

The scale has not moved in three weeks and I am eating to plan. Now what?

First check how honestly you are tracking and whether you have unconsciously slowed down during the day. If both are fine, this is a stall with a handful of typical causes, covered in the piece on weight loss plateaus.

Does meal timing matter?

For body composition, very little, as long as total calories and protein are where they should be. For training and sleep it can matter, since most people train better having eaten two or three hours earlier. Arrange meals so you can repeat the pattern for months.

Should training days and rest days be different?

Not necessarily. If you like the idea, keep the weekly total the same and move 200–300 calories of carbs from rest days to training days. Protein and fat stay the same every day.

The short version

Calculate BMR with Mifflin-St Jeor, multiply by an activity factor that errs on the modest side, then add or subtract 300–500 calories for your goal. Set protein at 1.6–2.2 g/kg, fat at 0.7–1.0 g/kg, and turn what is left into carbs.

The formula gives you the first number. The scale and three weeks give you the right one.

Then hold that plan for three weeks, read the weekly average, and adjust in steps of 150–200 calories. Redo the whole calculation after every 5–6 kg of weight change.