Calorie Surplus Calculator

Find your maintenance calories and the exact daily target that makes the scale move.

How the math works

Weight gain runs on one rule: eat more calories than your body burns, consistently. This calculator estimates what you burn in two steps, then adds the surplus that matches your goal.

Step 1: your baseline burn. The Mifflin-St Jeor equation estimates your basal metabolic rate, the calories your body uses just existing, from your sex, age, height, and weight. In head-to-head validation studies it beats the older Harris-Benedict formula, which is why dietitians default to it.

Step 2: your life multiplier. Your activity level scales that baseline up to your total daily energy expenditure (TDEE). Be honest here: a physical job counts, and so does being the person who never sits still. Underestimating activity is the number one reason "eating a lot" fails to move the scale.

Step 3: the surplus. A pound of body weight represents roughly 3,500 stored calories, so about 500 extra per day gains about a pound a week, and 250 gains about half a pound. Slower rates keep more of the gain lean; faster rates suit people who are clinically underweight and mainly need mass. Pair the target with the protein range shown and strength training so the surplus builds muscle, not just belly.

Next steps: split your target into macros with the bulking macro calculator, and see when you will arrive with the timeline calculator.

Frequently asked questions

How many extra calories do I need to gain weight?

A daily surplus of 250 to 500 calories above your maintenance level produces roughly 0.5 to 1 pound of gain per week for most people. Smaller surpluses gain slower but leaner; bigger surpluses gain faster but add more fat.

What formula does this calculator use?

It estimates your basal metabolic rate with the Mifflin-St Jeor equation, which validation studies rate as the most accurate of the common BMR formulas, then multiplies by an activity factor to estimate total daily energy expenditure (TDEE) and adds your chosen surplus.

The calculator number is not working for me. What now?

Formulas estimate; your scale decides. Eat the target for 2 to 3 weeks with weekly same-condition weigh-ins. If the trend has not moved, add about 200 calories and repeat. Two or three of these adjustments finds your real number.

Should teenagers use this calculator?

Ages 13 to 17 can use it as a rough starting point only. Adult formulas are less reliable during growth years, and a teen weight gain plan should involve a parent and the family doctor or pediatrician.

Sources

1. Mifflin MD et al., A new predictive equation for resting energy expenditure in healthy individuals, Am J Clin Nutr (1990): The BMR equation used by this calculator.
2. Frankenfield D et al., Comparison of predictive equations for resting metabolic rate, J Am Diet Assoc (2005): Mifflin-St Jeor as the most reliable of the common prediction equations.
3. Iraki J et al., Nutrition recommendations for bodybuilders in the off-season, Sports (2019): Modest surplus recommendations for gaining muscle with limited fat.
4. Morton RW et al., A systematic review of protein supplementation on resistance training outcomes, Br J Sports Med (2018): The 1.6-2.2 g/kg daily protein range behind the protein target.