Weight Gain Calculator
This calculator estimates weight change from the calories you eat above your maintenance level. On Calculators Wiki, it is meant for quick planning, not a promise of what the scale will do.
A common rule of thumb is that about 3,500 extra calories is roughly 1 pound of body fat, but real bodies do not follow that rule perfectly. Water retention, muscle gain, activity changes, and metabolism shifts can change the result.
If you want to compare against a target body mass, a BMI calculator can help put the number in context. For background on energy balance, see the NIH page on body weight and energy balance: nhlbi.nih.gov
How it's calculated
Basic method
- Daily surplus = calories eaten per day − maintenance calories per day
- Total surplus = daily surplus × number of days
- Estimated weight gain = total surplus ÷ 3,500 for pounds, or total surplus ÷ 7,700 for kilograms
Why the estimate can differ
- 3,500 calories per pound is only a rough rule of thumb.
- Early gains can include water and glycogen, not just fat.
- If you gain muscle or change activity, the scale can move differently.
Worked example
If your maintenance is 2,200 calories/day and you eat 2,500 calories/day for 30 days: - Daily surplus = 2,500 − 2,200 = 300 calories - Total surplus = 300 × 30 = 9,000 calories - Estimated gain = 9,000 ÷ 3,500 = 2.57 lb
In kilograms, the same example is 9,000 ÷ 7,700 = 1.17 kg.
Formula note
This is a simple energy-balance estimate, not a medical diagnosis. Real weight change can be slower or faster than the formula suggests.