Bulking Calculator
How it works
We estimate your maintenance calories, then add a surplus for your chosen rate of gain — about 550 calories a day per 0.5 kg per week. Protein is set from your bodyweight (choose the high-protein style for more), fat at ~30% of calories, and carbs fuel the rest.
A slower, leaner bulk (~0.25–0.5 kg/week) builds muscle while limiting fat gain. Track your weight and ease off if it climbs faster than planned.
Frequently asked questions
How many calories should I eat to bulk?+
Eat above your maintenance calories. A surplus of about 275–550 calories a day (0.25–0.5 kg gain per week) is enough to build muscle while limiting fat gain. This calculator adds the surplus for your chosen rate.
What's the difference between a lean bulk and a dirty bulk?+
A lean bulk uses a small surplus (~0.25 kg/week) to minimise fat gain; a dirty bulk uses a large surplus and adds more fat. For most people a slower, leaner bulk is the better trade-off.
How much protein do I need to build muscle?+
Around 1.6–2.0 g of protein per kg of bodyweight supports muscle growth. This calculator sets protein from your weight and lets you pick a high-protein split.
How fast should I gain weight when bulking?+
Roughly 0.25–0.5 kg per week. Faster than that is mostly fat, not muscle. Track your weight and drop the rate if it's climbing too quickly — Flun logs your food and weight trend for you.