About the Weight Gain Calculator
This weight gain calculator tells you how many calories to eat each day to put on weight at a chosen pace, how long it will take to reach your goal weight, and the date you would get there. It estimates your maintenance calories with the Mifflin-St Jeor equation and your activity level, then adds a daily surplus that matches your target rate of gain.
It is designed for people who are underweight or find it hard to gain, and for lifters planning a lean bulk. A slower rate — about 0.25–0.5 lb (0.1–0.25 kg) per week — keeps more of the gain as muscle for trained people, while beginners and those recovering from being underweight can often gain faster.
The surplus uses the common approximation of 3,500 kcal per pound of body weight. Muscle tissue actually contains fewer calories per pound than fat, but building it has an energy cost, so the rule is a practical starting point. Weigh yourself regularly and adjust your intake by 100–200 kcal if you gain faster or slower than planned.
With the default inputs, the daily calories to gain is 2,841 kcal/day. Change any value above to recalculate instantly.
How to use the weight gain calculator
- 1Enter your sex, age, height and current weight.
- 2Enter your goal weight and typical activity level.
- 3Pick a rate of gain — slower keeps the gain leaner.
- 4Set your start date to get a goal date.
- 5Eat the daily calorie target and adjust by 100–200 kcal after 2–3 weeks if needed.
Formula and method
Maintenance calories come from the Mifflin-St Jeor equation (10 × weight in kg + 6.25 × height in cm − 5 × age, +5 for men or −161 for women) multiplied by your activity factor. The daily surplus is the weekly rate of gain converted with the 3,500 kcal per pound rule and spread over seven days — for example 0.5 lb a week is 250 kcal a day.
The timeline divides the weight you want to gain by your weekly rate. Because maintenance calories rise as you gain, the calculator also shows the intake you would need at your goal weight to keep the same pace. The protein target uses 1.6 g per kg of current body weight, a level research links to maximal muscle gain for most people who lift.
- BMR
- Basal metabolic rate (kcal/day)
- 3,500
- Approximate kcal per pound of body-weight change
Worked examples
25-year-old man, 5 ft 10 in, 150 lb → 165 lb at 0.5 lb/week
At 68 kg and 177.8 cm his BMR is about 1,672 kcal, and moderate activity (×1.55) puts maintenance near 2,591 kcal. Half a pound a week needs 0.5 × 3,500 ÷ 7 = 250 kcal extra, so he eats about 2,841 kcal a day. Gaining 15 lb at that pace takes 30 weeks, reaching his goal on 3 August 2026.
30-year-old woman, 163 cm, 50 kg → 55 kg, lightly active, 0.23 kg/week
Her BMR is 10 × 50 + 6.25 × 163 − 5 × 30 − 161 ≈ 1,208 kcal and maintenance about 1,661 kcal. Adding 250 kcal gives about 1,911 kcal a day; at roughly 0.23 kg a week, 5 kg takes about 22 weeks.
Faster bulk: 150 lb → 170 lb at 1 lb/week
A 1 lb-per-week pace needs a 500 kcal daily surplus, or about 3,091 kcal a day to start. It reaches 170 lb in 20 weeks, but by then maintenance is higher, so about 3,232 kcal a day would be needed to keep gaining at the same rate.
Frequently asked questions
How many calories do I need to gain 1 pound a week?+
About 500 kcal a day above your maintenance calories, based on the 3,500 kcal per pound rule. For a leaner gain most lifters use a smaller surplus of 250–300 kcal a day, which is about half a pound a week.
How fast should I bulk?+
Beginners can often gain 0.5–1 lb (0.25–0.5 kg) a week with much of it muscle. Experienced lifters usually do better at 0.25–0.5 lb (0.1–0.25 kg) a week, because faster gains mostly add fat.
How much protein do I need to gain muscle?+
Research reviews find benefits up to about 1.6 g of protein per kg of body weight per day, with some people benefiting from up to 2.2 g/kg. Spreading it over 3–5 meals of 20–40 g each works well.
Why am I not gaining weight even though I eat a lot?+
Most people who struggle to gain overestimate how much they eat. Track intake for a week, add calorie-dense foods such as nuts, oils, whole milk and smoothies, and increase intake by 200–300 kcal if the scale does not move within two weeks.
Is it healthy to gain weight quickly?+
Rapid gain mostly adds body fat and can raise blood lipids and blood pressure over time. If you are underweight because of illness or an eating disorder, work with a doctor or dietitian rather than following a general calculator.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.