Build Muscle
Weight Gain Calculator
To gain weight, eat 250 to 500 calories above your maintenance calories each day. A 250 kcal surplus adds roughly 0.25 kg per week. This calculator finds your maintenance, adds your chosen surplus, and projects a timeline to your goal weight.
Your plan
Learn how this works
How Many Calories Should You Eat to Gain Weight?
How a calorie surplus drives weight gain, how big it should be for a lean bulk, and how fast you can add muscle.
Read the guideKey facts about gaining weight
- A 250 kcal daily surplus produces roughly 0.25 kg (0.5 lb) of weight gain per week.
- Healthy lean gain pace is about 0.25 to 0.5 kg per week; faster gains are mostly fat.
- One kilogram of body mass stores approximately 7700 calories of energy.
- Protein at 1.6 to 2.2 grams per kilogram plus progressive resistance training makes the gain muscle instead of fat.
How many calories do you need to gain weight?
Gaining weight follows the same energy balance as losing it, just in reverse. When you eat more than you burn, your body stores the extra energy and you gain. The size of that surplus decides how fast you gain and, importantly, how much of the gain is muscle versus fat. This calculator finds your maintenance calories with the Mifflin-St Jeor equation (1990), adds the surplus you choose, and projects your progress toward a goal weight. The constants live on the methodology page.
Choosing your surplus
For a lean gain that maximizes muscle and minimizes fat, a small surplus of about 250 calories a day works well, adding roughly a quarter of a kilogram a week. A standard bulk of 500 gains faster, and larger surpluses gain faster still but add more fat, since muscle can only be built so quickly no matter how much you eat. We use the estimate that one kilogram of body mass holds about 7700 calories to turn your surplus into a weekly rate and a projected date.
| Preset | Daily surplus | Weekly gain (kg) | Weekly gain (lb) |
|---|---|---|---|
| Lean | 250 kcal | 0.23 | 0.5 |
| Standard | 500 kcal | 0.45 | 1.0 |
| Fast | 750 kcal | 0.68 | 1.5 |
Worked example
A 24 year old man at 65 kg and 178 cm who trains moderately has a maintenance near 2600 calories. Adding a lean 300 calorie surplus sets his target near 2900 calories a day, gaining about 0.27 kg a week. To reach a 72 kg goal, roughly 7 kg of gain, the timeline projects about 26 weeks, or half a year, of steady lean bulking.
How do you make the gain muscle, not just fat?
A surplus only builds muscle if you give your body the raw materials and the stimulus. Keep protein high, around 1.6 to 2.2 grams per kilogram, using the protein calculator, set your full split with the macro calculator, and train with progressive resistance. Track your lean mass over time with the FFMI calculator, and if you would rather add muscle without gaining much weight at all, the body recomposition calculator is the better starting point.
Why is the scale not moving?
If the scale is flat despite eating what feels like a lot, intake is usually lower or activity higher than it seems. Track honestly for a week and add another 200 to 300 calories if needed. Recalculate as you gain, since maintenance rises with body weight. And if your low weight is unexplained or accompanied by other symptoms, talk to a doctor before pushing calories; a calculator is for healthy gaining, not diagnosing.
Limitations of this calculator
The maintenance figure underneath your surplus is an estimate within about 10 percent, so your real starting point may need adjusting from the scale. The 7700 kcal per kg conversion is an average, and how much of a surplus becomes muscle versus fat depends on training, protein, sleep, and genetics, not calories alone, so the timeline is a projection rather than a promise. This tool is for healthy weight gain; unexplained low weight or difficulty gaining despite eating well can have medical causes and deserves a doctor's input.
Sources and references
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure. Am J Clin Nutr. 1990. PubMed 2305711
- Slater GJ, et al. Is an energy surplus required to maximize skeletal muscle hypertrophy associated with resistance training? Front Nutr. 2019. PubMed 31482093
- Garthe I, et al. Effect of nutritional intervention on body composition and performance in elite athletes. Eur J Sport Sci. 2013. PubMed 24479489
Surplus and energy constants are documented on the methodology page.
Frequently asked questions
How many calories to gain weight?
Add a surplus above maintenance: about 250 calories daily for a lean gain of roughly 0.25 kg per week, up to 500 for a faster bulk. The tool adds your surplus to TDEE and projects the timeline.
How fast should I gain weight?
For muscle with minimal fat, 0.25 to 0.5 kilograms per week, slightly faster for true beginners. Gaining much faster mostly adds fat, since muscle can only be built so quickly.
What should I eat to gain weight healthily?
Build the surplus from nutritious, calorie dense foods: whole grains, nuts, dairy, olive oil, lean proteins. Keep protein at 1.6 to 2.2 g/kg and train with progressive resistance so the gain includes muscle.
Why am I not gaining weight even eating a lot?
Usually intake is lower or activity higher than it feels. Track honestly for a week; if the scale is flat, add 200 to 300 calories a day. Inconsistent tracking is the most common culprit.
Can I gain muscle without gaining fat?
Beginners and returners can, essentially recomposition. Most others gain a little fat alongside muscle in a surplus, which is normal and can be trimmed later with a short cut.