How many calories do I need to gain weight?

Most people need a surplus of about 250-500 calories above their maintenance (TDEE) for a lean, steady gain of 0.25-0.5 lb per week. This calculator estimates your maintenance number and adds the surplus for your chosen goal rate.

Is the Mifflin-St Jeor equation accurate?

It is the most accurate widely-used formula for predicting resting energy needs in healthy adults, but it is still an estimate (typically within about 10%). Use the result as a starting point and adjust based on real weight changes over 2-3 weeks.

How fast can I safely gain weight?

For most people, 0.25-1 lb per week is a sensible range. Slower gains minimize fat gain and work well for lean bulking; faster gains suit those who are significantly underweight when paired with resistance training.

How much protein should I eat to build muscle?

Research supports roughly 0.7-1 gram of protein per pound of body weight per day (about 1.6-2.2 g/kg) when training to build muscle in a calorie surplus. This calculator defaults to about 1 g per pound.

Why am I not gaining weight even though I'm eating more?

Usually because you are not actually in a surplus - people underestimate maintenance and overestimate intake - or your daily activity burns more than expected. Track intake honestly for a week and add calorie-dense foods if the scale isn't moving.

Weight Gain Calorie Calculator

Find out exactly how many calories you need to gain weight at your chosen pace. This calculator estimates your BMR with the Mifflin-St Jeor equation, scales it to your TDEE, adds a calorie surplus for your goal rate, and splits the total into protein, fat, and carb targets.

Age (years)

Sex (for BMR formula)

Height

Weight

Activity level

Goal: weight gain per week

Your daily targets

To gain weight at your selected rate, aim for about:

0 kcal/day

BMR

Maintenance (TDEE)

Surplus

Suggested macros

0 g

Protein

0 g

Fat

0 g

Carbs

Protein is set at ~1 g per pound of current body weight (a research-supported range for building muscle in a surplus). Fat is ~25% of total calories; the rest of your calories come from carbohydrates to fuel training.

Estimate only. These numbers are a starting point, not a prescription. Track your weight for 2-3 weeks and adjust by 100-200 kcal if you are gaining faster or slower than your goal. This tool is for general information and is not medical advice. Talk to a doctor or registered dietitian before changing your diet, especially if you are underweight, have a medical condition, or take medication.

How this calculator works

Gaining weight comes down to one rule: you must eat more calories than your body burns. The challenge is knowing your real "burn" number. This tool estimates it in three steps.

1. Basal Metabolic Rate (BMR) — Mifflin-St Jeor

Your BMR is the energy your body uses at complete rest just to stay alive. We use the Mifflin-St Jeor equation, which the Academy of Nutrition and Dietetics has identified as the most accurate predictive resting-energy equation for healthy adults:

Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161

2. Total Daily Energy Expenditure (TDEE)

We multiply BMR by an activity factor (1.2 sedentary up to 1.9 extra active) to estimate the calories you burn in a typical day. This is your maintenance level — eat this and your weight stays roughly the same.

3. Calorie surplus for weight gain

One pound of body weight is roughly 3,500 calories, so a surplus of ~500 kcal/day adds about 1 pound every two weeks (0.5 lb/week). We add the surplus that matches your chosen goal rate. Slower rates (0.25-0.5 lb/week) favor lean gains with less fat; faster rates put on weight quicker but add more fat.

Sources: Mifflin MD, St Jeor ST, et al. "A new predictive equation for resting energy expenditure in healthy individuals." Am J Clin Nutr. 1990 (PubMed) · Academy of Nutrition and Dietetics · NIH / NIDDK Weight Management · CDC Adult BMI.

Frequently asked questions

How many calories do I need to gain weight?: Most people need a surplus of about 250-500 calories above maintenance (TDEE) for a lean, steady gain of 0.25-0.5 lb per week. This calculator estimates your maintenance number and adds the surplus for your chosen goal rate.
Is the Mifflin-St Jeor equation accurate?: It is the most accurate widely-used formula for predicting resting energy needs in healthy adults, but it is still an estimate (typically within ~10%). Use the result as a starting point and adjust based on real-world weight changes over 2-3 weeks.
How fast can I safely gain weight?: For most people, 0.25-1 lb per week is a sensible range. Slower gains (0.25-0.5 lb/week) minimize fat gain and work well for "lean bulking." Faster gains are appropriate if you are significantly underweight, but pair them with resistance training so more of the weight is muscle.
How much protein should I eat to build muscle?: Research supports roughly 0.7-1 gram of protein per pound of body weight per day (about 1.6-2.2 g/kg) when training to build muscle in a calorie surplus. This calculator defaults to ~1 g/lb.
Why am I not gaining weight even though I'm eating more?: The two most common reasons are (1) you are not actually in a surplus — people routinely underestimate maintenance and overestimate intake, and (2) your activity or NEAT (fidgeting, walking) burns more than you think. Track intake honestly for a week and increase calorie-dense foods if the scale isn't moving.

Not medical advice. WeightGain.us provides general educational information only. It is not a substitute for professional medical or nutrition advice, diagnosis, or treatment. Always consult a qualified physician or registered dietitian before starting any diet or supplement program. Operator: Mustafa Bilgic.