What this tool does
A calorie surplus is eating above maintenance so resistance training has energy to build tissue. This calculator estimates your TDEE from height, weight, age, sex, and activity, then adds your chosen surplus percent (5–20%). You get a daily target, the extra calories above TDEE, and a rough weekly weight-gain line using the same 7,700 kcal/kg sketch as our deficit tools. It is for lifters in a bulk phase — not for adding calories without progressive training.
How it works
Mifflin-St Jeor (1990) estimates BMR; an activity factor (1.2–1.9) gives TDEE. Target = TDEE × (1 + surplus%/100). Beginners can tolerate the upper end; trained lifters usually stay near 5–12% so fat gain stays manageable. Pair the number with protein in the muscle band (about 1.6–2.2 g/kg per ISSN guidance) so the surplus has amino acids to work with.
Formula and methodology
BMR (Mifflin-St Jeor): men 10×kg + 6.25×cm − 5×age + 5; women 10×kg + 6.25×cm − 5×age − 161. TDEE = BMR × activity. Target = TDEE × (1 + surplus%/100). Rough kg/week ≈ (target − TDEE) / (7,700/7). The weekly line is a planning sketch — tissue gained is mixed muscle, fat, glycogen, and water.
How to interpret the result
5–8% is a lean-bulk nudge for trained lifters. 10–15% is the usual starting band for most bulk phases. 15–20% shows up faster on the scale and faster around the waist if training does not keep up. If waist jumps weekly while main lifts stall, trim 100–200 kcal. Rest days still count toward the weekly surplus average — you do not “earn” food only on training days.
Example
Worked example: 80 kg, 180 cm, age 30, male, moderately active → Mifflin-St Jeor TDEE ≈ 2,760 kcal. A 10% surplus → about 3,040 kcal/day, roughly 280 kcal extra, paper gain near 0.25 kg/week. Pair with ~150 g protein (≈1.9 g/kg). That extra is a yogurt and a banana — not a second dinner as a personality.
Common mistakes
- Stacking a 15% surplus on a TDEE that was already above maintenance.
- A 20% surplus with two easy gym sessions and calling it a bulk.
- Skipping protein because “calories are anabolic.”
- Changing the surplus every time morning weight ticks up from glycogen or creatine.
- Cutting all carbs “to stay lean” while in a surplus — you just made training worse.
When this estimate may be off
- You are not training with progressive overload.
- Activity in the dropdown was theater, so TDEE is inflated before the surplus lands.
- Appetite drugs, illness, pregnancy, or other states this adult equation ignores.
- Weight gain is mostly edema, menstrual water, or a new creatine loading week.