How many calories should I eat to build muscle?

Maintenance +12.5%. Maintenance is your resting energy (Mifflin–St Jeor) times an activity factor of 1.45–1.65 depending on how often you train. On an 80 kg man training four times a week that is roughly 2,900–3,000 kcal; the calculator gives your own number.

How big a deficit should I run to lose fat?

−17.5% of maintenance, and never more than −25% whatever you type. A bigger deficit costs muscle, and muscle is the point.

How much protein per day?

1.8 g per kg of body weight when building, 2 g/kg on a recomp and 2.2 g/kg in a deficit — 176 g a day for an 80 kg lifter who is cutting.

Why will it not give me a lower number?

The −25% floor is enforced before any number is shown, and under 18 or under a BMI of 18.5 the calculator shows maintenance instead of a deficit. Faster is not better here.

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How many calories should you eat to bulk or cut?

Short answer

Eat maintenance +12.5% to build muscle, −17.5% to lose fat (never below −25%), or maintenance to recomp — with 1.8, 2.2 and 2 g of protein per kg of body weight respectively. Maintenance is Mifflin–St Jeor × 1.45–1.65 for your training frequency.

Daily calories and protein for building muscle, losing fat, or doing both at the same body weight. It runs the exact function the Month6 app uses, so the number here is the number you would see there.

Goal

Sex

Units

Age

Sessions / week

Weight

Height

Daily calories

2,950 kcal

Maintenance is about 2,650 kcal

Daily protein

126 g

An estimate for healthy adults, not medical advice. How every number is made, with its citations: Sources & method.

What each goal does

Calories, protein and weekly weight change by goal
Goal	Calories	Protein	Scale, per week
Build muscle (bulk)	+12.5%	1.8 g/kg	+0.375% of body weight
Lose fat (cut)	−17.5%	2.2 g/kg	−0.625% of body weight
Both (recomp)	maintenance	2 g/kg	0

Protein per day, by body weight

Daily protein target by body weight and goal
Body weight	Build	Recomp	Cut
60 kg	108 g	120 g	132 g
70 kg	126 g	140 g	154 g
80 kg	144 g	160 g	176 g
90 kg	162 g	180 g	198 g
100 kg	180 g	200 g	220 g

How the number is made

Resting energy comes from the Mifflin–St Jeor equation. That is multiplied by an activity factor stepped by how often you train (1.45 for two or three sessions a week, 1.55 for four or five, 1.65 for six), which gives maintenance. Your goal then scales it: ×1.125 to build muscle, ×1.0 to recomp, ×0.825 to lose fat. The result is rounded to the nearest 50 kcal, because the inputs are not accurate enough to justify more.

Protein is set per kilogram of body weight: 1.8 g/kg when building, 2 g/kg for a recomp, and 2.2 g/kg in a deficit, where protein does the most to hold on to muscle.

Why it will not give you a crash diet

A floor is enforced before any number is shown: the target never drops below 75% of your estimated daily expenditure. Below a BMI of 18.5, or under the age of 18, the calculator will not set a deficit at all and shows maintenance instead. Faster is not better here — an aggressive deficit costs muscle, and muscle is the point.

How to use it

Treat the number as a starting estimate, hold it for two weeks, and watch the trend in your body weight rather than any single day. Building: aim for roughly a quarter to half a percent of body weight gained per week. Losing fat: half to three-quarters of a percent lost per week. If the trend is off, move calories by 100–150 and give it another two weeks.

Questions

See your six-month body. Then go earn it.

A calorie target only works if it is checked against what actually happens. Month6 plots your weekly weigh-in against a six-month projection and moves this number when you drift off it.