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How many calories does a skinny guy need to build muscle?

A skinny guy needs about 10-15% more than his maintenance calories to build muscle. For most guys that's 200-300 extra calories a day (beginners can go up to 15-20%). A rough start for maintenance is your weight in kg × 40. Then weigh yourself for 2-3 weeks and aim for 0.2-0.5 kg (0.5-1 lb) a week.

Why doesn't "just eat more" work for skinny guys?

Because "more" isn't a number.

You eat a huge dinner, feel stuffed, skip lunch the next day without noticing, and the scale doesn't move. Then you tell yourself you've got bad genetics.

The trick isn't eating more. It's knowing how many calories you actually need, and hitting that number most days.

How do I work out my maintenance calories?

Quick estimate: your bodyweight in kg × 40 (or in lb × 18). A 65 kg guy lands around 2,600 calories a day. Add 200-300 on top and he's at roughly 2,800-2,900.

That's an estimate, not the truth. The real test is the scale: eat that number for 2-3 weeks, weigh yourself, and see what happens. The calculator on this site gives you a starting point too.

How fast should a skinny guy gain weight?

• Upper limit: 0.5-1% of your bodyweight per week.
• In real life: about 0.2-0.5 kg (0.5-1 lb) per week.
• If you want to keep fat to a minimum: 0.5-1 kg (1-2 lb) per month.

Scale not moving after 2-3 weeks? Add a little more food. Shooting up much faster than this? Pull back a little.

Isn't a bigger surplus faster?

The scale goes up faster, yes. Your muscles don't. With a "dirty bulk" of 1,000 calories or more over maintenance, a lot more of the weight you gain is fat. You end up softer, not bigger where you want it.

My case

I went from 63 kg to 83 kg (139 to 183 lb) in five years, most of it muscle. It took that long because I was guessing. I never knew my number. It wasn't a genetics problem. It was a knowledge problem.

Work out your numbers →

Read next: Why can't I gain weight even though I eat a lot? and How much protein do I need as a skinny guy?