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Lean bulk calculator

The daily surplus that actually builds muscle, the rate the scale should move, and a 12-week projection that splits gains into muscle vs fat based on your training age.

Units
Daily surplus

Daily food budget

2923

kcal/day · TDEE 2673 + surplus 250

BMR
1725 kcal
TDEE
2673 kcal
Weekly rate
+0.50 lb/wk
Projected at 12 weeks
171.0 lb (+6.0)
of which muscle
~2.8 lb
of which fat / water
~3.2 lb

Muscle ceiling note

At your training stage, the realistic ceiling is roughly 1.00 lb of muscle per month. Over 12 weeks, that caps muscle gain near 2.8 lb. Anything the surplus delivers above that lands as fat.

Still well within the newbie window. A clean surplus pays back almost fully.

Compare surpluses

200 kcal

+0.40 lb/wk

4.8 lb in 12 wk

~2.8 lb muscle · ~2.0 lb fat

250 kcal

+0.50 lb/wk

6.0 lb in 12 wk

~2.8 lb muscle · ~3.2 lb fat

350 kcal

+0.70 lb/wk

8.4 lb in 12 wk

~2.8 lb muscle · ~5.6 lb fat

500 kcal

+1.00 lb/wk

12.0 lb in 12 wk

~2.8 lb muscle · ~9.2 lb fat

TDEE rises as you add mass, so re-run every 5% bodyweight change. The muscle-vs-fat split is bounded by the natural ceiling for your training age — a bigger surplus moves the scale faster but mostly via fat once the ceiling is hit. See the lean bulk math and muscle-per-month posts for context.

Formula & assumptions

BMR uses the Mifflin-St Jeor equation, then activity level turns resting metabolism into estimated TDEE:

BMR_male   = 10·W + 6.25·H - 5·A + 5
BMR_female = 10·W + 6.25·H - 5·A - 161
TDEE       = BMR × activity multiplier
W = body weight (kg), H = height (cm), A = age (years)

Daily food budget = TDEE + surplus. The classic 3,500 kcal-per-pound conversion gives the weekly rate:

weekly_rate_lb = (surplus × 7) / 3500
gain_12wk_lb   = weekly_rate_lb × 12

Muscle vs fat split is bounded above by the natural muscle-gain ceiling for your training age. Lyle McDonald's well-known synthesis and the evidence summarised by Helms et al. (2014) and Aragon & Schoenfeld (2013) both converge on similar numbers:

Untrained / novice    ~1.0-1.5 lb/month muscle
Novice (1-2 years)    ~1.0    lb/month muscle
Intermediate (3-5y)   ~0.5    lb/month muscle
Advanced (5y+)        ~0.25   lb/month muscle

Once the surplus delivers more weight than the muscle ceiling can absorb, the remainder lands as fat. That is the diminishing-returns curve behind every "dirty bulk" regret post.

Caveat: TDEE rises as you add mass, and these are ceilings, not promises. Sleep, training quality, protein intake, and stress all sit underneath the curve. Re-run every 5% bodyweight change.

References

Mifflin, M. D. et al. (1990). A new predictive equation for resting energy expenditure in healthy individuals. The American Journal of Clinical Nutrition, 51(2), 241-247.

Helms, E. R., Aragon, A. A., & Fitschen, P. J. (2014). Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. Journal of the International Society of Sports Nutrition, 11, 20.

Aragon, A. A., & Schoenfeld, B. J. (2013). Nutrient timing revisited: is there a post-exercise anabolic window? Journal of the International Society of Sports Nutrition, 10(1), 5.

Hall, K. D. (2008). What is the required energy deficit per unit weight loss? International Journal of Obesity, 32(3), 573-576.

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