Weight Gain Calculator (Calorie Surplus)

Work out a daily calorie target, surplus, protein range and timeline to reach a goal weight at a lean-gain pace you choose.

Last updatedHow we build & check our tools
lbs
lbs
in
%
Results will appear here once you enter your values.

How the calorie target is built

The calculator starts from maintenance, the calories you burn in a normal day, and adds a surplus sized to the rate of gain you pick. Maintenance comes from the Mifflin-St Jeor equation, the resting-energy formula most dietitians use: 10 x weight in kg + 6.25 x height in cm - 5 x age, plus 5 for men or minus 161 for women. A 30-year-old man who weighs 80 kg and stands 180 cm tall burns about 1,780 kcal at rest.

That resting figure is multiplied by an activity factor, from 1.2 for a desk job with no training up to 1.9 for hard daily training. At the moderate factor of 1.55, the same man maintains his weight on roughly 2,760 kcal a day.

The surplus. Your weekly gain target is a percentage of body weight. At 0.25% per week the 80 kg man aims for 0.2 kg a week. Using the rough planning figure of 7,700 kcal per kilogram of gained tissue, that is 1,540 extra kcal a week, or about 220 kcal a day, so his target becomes about 2,980 kcal. The timeline divides the weight still to gain by the weekly rate: 5 kg at 0.2 kg a week is 25 weeks.

Choosing a rate: why slower gains stay leaner

Muscle can only be built so fast, so eating far above maintenance mostly adds fat. A 2019 review of off-season bodybuilding nutrition by Iraki and colleagues suggested gaining about 0.25-0.5% of body weight per week, with less-trained lifters toward the top of that range and experienced lifters toward the bottom. This tool labels anything above 0.5% as aggressive and caps the input at 1% per week.

  • Protein: the results show 1.6-2.2 g of protein per kg of body weight a day, the range most sports-nutrition research supports for building muscle while in a surplus.
  • Training: a surplus without resistance training is just weight gain. Progressive strength training is what directs extra energy toward muscle.
  • Adjust with data: weigh yourself several mornings a week and compare weekly averages. If you gain faster than planned, cut 100-200 kcal; if the scale has not moved in two to three weeks, add the same.

Common mistakes when trying to gain weight

  • Treating 7,700 kcal per kg as exact. The energy cost of gained tissue depends on how much is muscle, fat and water, and your body adapts to extra food. Kevin Hall's modeling work showed why fixed rules like this drift over time. Use the number to start, then adjust to your real weigh-ins.
  • Reading day-to-day scale jumps as fat. Salt, carbohydrate and training can move body weight by 1-2 kg overnight. Judge progress on weekly averages.
  • Overstating activity. Picking "very active" because you train hard for an hour can overshoot maintenance by several hundred calories. If unsure, choose one level lower.
  • Relying on liquid calories alone. Shakes help if appetite is the limit, but meals built around protein, starches and healthy fats make the surplus easier to sustain.
  • Ignoring the reason you are underweight. Unexplained weight loss, a low appetite from illness or an eating disorder needs medical care, not a calorie target.

Frequently Asked Questions

Common questions about the Weight Gain Calculator (Calorie Surplus)

Eat your maintenance calories plus a surplus. For a lean pace of 0.25-0.5% of body weight per week, that is usually about 200-500 extra kcal a day. This calculator estimates maintenance with Mifflin-St Jeor and sizes the surplus from your chosen rate.

Sources & References

Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247

Source of the Mifflin-St Jeor resting energy equation used for maintenance calories.
→Source: American Journal of Clinical Nutrition (PubMed)

Iraki J et al. Nutrition Recommendations for Bodybuilders in the Off-Season: A Narrative Review. Sports. 2019;7(7):154

Supports the 0.25-0.5% of body weight per week gain rate and protein guidance.
→Source: Sports (PubMed)

Hall KD. What is the required energy deficit per unit weight loss? Int J Obes. 2008;32(3):573-576

Explains why a fixed calories-per-kg rule (about 7,700 kcal/kg) is only an approximation.
→Source: International Journal of Obesity (PubMed)

Explore More Tools

Explore these related tools for your next step.

body-nutrition

Bmi Calculator - Free Online Tool

Calculate your Body Mass Index (BMI) to assess if your weight is in a healthy range. Uses WHO classifications and provides visual feedback.

Try it now
body-nutrition

Calorie Calculator - Free Online Tool

Calculate your daily calorie needs based on the Mifflin-St Jeor equation. Includes BMR, TDEE, and macro suggestions for your goals.

Try it now
body-nutrition

Army Body Fat Calculator (One-Site Tape Test)

Estimate your body fat with the Army's one-site abdominal tape equation, apply AR 600-9 rounding, and see whether you meet the maximum for your age group.

Try it now
body-nutrition

Waist-to-Height Ratio Calculator

Divide your waist by your height to check central adiposity against the NICE NG246 bands, and see the waist size that keeps you under the 0.5 line.

Try it now
body-nutrition

BMI Percentile Calculator for Kids & Teens

Find a child's BMI-for-age percentile (ages 2 to 20) from CDC growth charts, including CDC's extended method for BMIs above the 95th percentile.

Try it now
body-nutrition

Height & Weight Percentile Calculator for Kids (2-20)

Find your child's height-for-age and weight-for-age percentiles from the CDC 2000 Growth Charts, for boys and girls aged 2 to 20, in inches and pounds or centimeters and kilograms.

Try it now