A small surplus is enough: calories do not build muscle, they only permit it. Why four weeks of scale data beat any calculator you can find.
The honest answer: small. Building muscle does not need a mountain of calories, it needs a slight plus over your daily requirement — in practice around 200 to 400 kcal more per day. That is roughly a tub of skyr with oats and a banana. This range is a practical experience value, not a study figure — which is exactly why four weeks of checking matter more than the calculation you start with.
Why not more? Because calories do not build muscle. Training sets the stimulus, protein delivers the building material — 1.4 to 2.0 g per kilogram of body weight per day [3]. Above roughly 1.62 g/kg, a meta-analysis of 49 studies with 1,863 trainees found no further gain in fat-free mass [4]. The calories on top are merely permission to build at all.
Straight talk: a bulk is not a free pass, it is a boring calculation with a lot of patience attached. Anything you add beyond the small surplus most likely lands as fat — and has to come off again later.
The equation: 10 × weight in kg + 6.25 × height in cm − 5 × age, plus 5 for men, minus 161 for women [1]. That gives resting metabolic rate. Multiplied by an activity factor — roughly 1.4 to 1.8 with regular training, which is counselling practice, not a study figure — you get your daily requirement.
Now the part almost everyone skips: a systematic review found that Mifflin-St Jeor hits measured resting metabolic rate within ±10 % more often than any other equation tested [2] — with explicitly relevant deviations in individual cases. At an estimated requirement of 2,800 kcal, 10 % is around 280 kcal. That is roughly the size of your planned surplus. So the starting number is a hypothesis, not a target.
Put yourself in the 1.4 to 2.0 g/kg range [3]; in practice 1.6 to 1.8 is a good place for people who lift. Spread it across at least four meals at roughly 0.4 g/kg per meal [5] — at 80 kg that is roughly 32 g four times a day.
One thing for your expectations: in the meta-analysis, the effect of additional protein was larger in trained individuals and decreased with rising age [4]. Protein is the prerequisite, not the amplifier.
Add 200 to 400 kcal to your estimate — as an experience value, not a prescription. The simplest source is carbohydrates around training: a bigger portion of rice, pasta or potatoes, a second slice of bread, another spoon of peanut butter.
Then stay there for four weeks. Not three days. Body weight swings by one to two kilos through water, salt and gut content — any adjustment before week four corrects noise, not signal.
Weigh yourself several times a week under the same conditions and take the weekly average. Only that average against last week's is information.
If nothing at all has moved after four weeks, add another 100 to 200 kcal. If it climbs noticeably faster than you would like, take them back out. And do not only weigh: training loads, repetitions and body measurements are the better indicators of whether what you are gaining is actually muscle.
If you would rather not do the arithmetic yourself: the nutrition plan in the Lab uses exactly this equation and adds the surplus automatically when the goal is muscle gain.
Losing fat and building muscle at the same time works best for beginners, for people returning after a long break and at higher body fat levels. That is practical experience, not a proven rule — but it explains why some people appear to outwit physics in their first year and advanced lifters do not.
You should end the building phase when your waist grows faster than your training loads. That is the most honest stop signal there is.
This guide explains relationships, it does not replace medical or dietetic advice. With metabolic, cardiovascular, kidney or liver conditions, with diabetes, during pregnancy and breastfeeding, or while taking medication, any deliberate change in body weight belongs under medical supervision.
Unplanned, rapid weight gain with fluid retention, shortness of breath or heavy fatigue is not a training success, it is a reason to book an appointment.
If eating, gaining or controlling numbers starts running your day, or if your body image is putting you under pressure, talk to your doctor, a registered dietitian or a counselling service. Calculations like these are not intended for growing children and adolescents.
Do not only count calories, count repetitions. Keep a simple training log with the load and reps of your four most important lifts.
The reason: a working build-up shows in the log before it shows in the mirror. If your reps at the same load rise over four to six weeks, the surplus is doing its job. If they stay flat while the scale climbs, the surplus is too big or the training too small — and you know immediately which of the two dials to turn.
Considerably slower than the market suggests. Robust monthly figures barely exist, and they depend heavily on training age, chronological age and genetics. In practice: beginners see the biggest jumps in the first year, after which it continues in small steps. So judge progress over months and by your training loads, not by the scale.
For beginners, for people returning after a break and at higher body fat levels, losing fat and building muscle simultaneously is realistic. For advanced trainees it becomes unlikely — there it is usually more efficient to separate phases. This classification is practical experience, not a proven rule.
No, that is a convention, not a law. If you are comfortable with your current body fat level and run a moderate plus, you can stay in a slightly building phase for a very long time. Separate phases mainly make sense once you are advanced and progress has become small.
1.4 to 2.0 g per kilogram of body weight per day covers the requirement [3]; above roughly 1.62 g/kg the meta-analysis found no further gain in fat-free mass [4]. Spread the amount across at least four meals at roughly 0.4 g/kg [5] rather than catching up with one huge evening portion.
By three signs at once: the scale climbs faster than about half a kilo a month, your waist grows noticeably with it, and your training loads do not follow. Then take out 100 to 200 kcal and watch for another four weeks. A build-up that feels fast is usually a fat gain.
Losing Fat Without Losing Performance