Lean gain calculator
Three numbers, in order: what your body burns at rest (BMR), what it burns in a normal day (TDEE), and how much to eat to gain weight slowly at the pace you choose.
Choose your pace
The surplus is how far above your TDEE you eat. Slower gains mean less fat comes along with the muscle. Faster paces add weight sooner, but more of it is likely to be fat.
Every activity level at a glance
Same body, different lifestyles. Use this to see how much your activity level moves the numbers.
| Activity level | Maintain (TDEE) | Target |
|---|
How it works, and how to do it by hand
The formula (Mifflin-St Jeor)
This is the most widely recommended equation for healthy adults and is the one used above.
Women: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161
Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5
To convert: pounds ÷ 2.205 = kg. Inches × 2.54 = cm.
TDEE = BMR × activity multiplier
Target = TDEE + surplus
Activity multipliers
- 1.2 Sedentary: desk job, little or no exercise
- 1.375 Lightly active: exercise 1 to 3 days a week
- 1.55 Moderately active: exercise 3 to 5 days a week
- 1.725 Very active: hard exercise 6 to 7 days a week
- 1.9 Extremely active: physical job plus hard training
Worked example
A 40-year-old woman, 165 lb (74.8 kg), 5 ft 5 in (165.1 cm), exercising about 2 days a week.
BMR = 748 + 1,032 − 200 − 161 = 1,419
TDEE = 1,419 × 1.375 = 1,951
Target for about 0.5 lb a week = 1,951 + 250 = 2,201
Where the surplus numbers come from
A common rule of thumb is that about 3,500 calories equals 1 lb of body fat (about 7,700 per kg). So a 500-calorie daily surplus adds up to 3,500 a week, or roughly 1 lb of body weight. This is an approximation, and it only counts scale weight. Muscle is built slowly, and the faster the scale climbs, the larger the share that tends to be fat. That is why a small surplus usually beats a big one.
Getting the most from a surplus
Extra calories only tend toward muscle when your body has a reason to build it, which means regular resistance training. Without it, most of a surplus is stored as fat. The 4-day workout split on this site is one way to put the calories to work.
Weigh yourself at the same time of day, a few times a week, and judge the trend over 2 to 3 weeks rather than day to day. If you're gaining faster than the pace you picked, trim 100 to 200 calories. If the scale isn't moving, add that much instead.
These are estimates, typically within about 10% of what your body really burns. Weigh yourself regularly for 2 to 3 weeks, and if the scale isn't moving the way you expect, adjust by 100 to 200 calories. Recalculate after you've gained 10 lb or more. This is general information, not medical advice. If you are pregnant or breastfeeding, under 18, or have a medical condition, or you're underweight and aren't sure why, talk with a doctor or registered dietitian before eating in a surplus.