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Bulking Calculator: Calories and Macros for a Lean Bulk
Your maintenance calories, the surplus for the bulk you choose, the protein, carbohydrate and fat to fill it, and how fast the scale should move.
Short answer
Maintenance plus a surplus: about 250 calories a day for a lean bulk, 500 for a standard bulk and 750 for an aggressive one. For a 25-year-old, 178 cm (5 ft 10 in), 70 kg (154 lb), moderately active man, maintenance is about 2,620 calories, so a lean bulk is about 2,870. Aim to gain 0.25–0.5% of body weight a week — 0.18–0.35 kg (0.4–0.8 lb) at 70 kg.
Bulking is a calorie surplus with a purpose: enough extra energy to support muscle growth from training, without so much that most of the gain is fat.
The arithmetic is maintenance plus a surplus. The harder part is choosing the surplus, and then eating it every day, including the days you are not hungry.
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Bulking Calculator
Your maintenance calories, the surplus for the bulk you want, and the protein, carbohydrate and fat that go with it.
If you know it, maintenance is worked out from lean mass (Katch-McArdle) instead of Mifflin-St Jeor.
Inside the recommended rate
2873 kcal a day, every day, is the hard part of a bulk.
Gain Weight is one of SlimAI's three goals, with the same 250, 500 and 750 calorie surpluses. It counts every meal against the target and recalculates it when your weight changes, so the surplus keeps up as you grow.
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A starting estimate for healthy adults who lift. Adjust after two to three weeks of real weigh-ins. If you are underweight because of illness, appetite loss or an eating disorder, gaining weight is a medical question first. Not medical advice.
Choosing Your Surplus
All three build muscle if you train hard enough. They differ in how much fat comes with it and how quickly the scale moves.
+250 kcal a day
About 0.23 kg (0.5 lb) a week in theory. The slowest scale change and the smallest share of fat, which suits anyone who is already at a healthy weight and does not want a long cut afterwards.
+500 kcal a day
About 0.45 kg (1 lb) a week in theory. A reasonable choice for beginners, who gain muscle fastest, and for people who struggle to gain at all.
+750 kcal a day
About 0.7 kg (1.5 lb) a week in theory. Mostly useful if you are underweight. For anyone else, a large share of the extra weight will be fat.
Lean bulk or dirty bulk
A review of nutrition for natural bodybuilders recommends a surplus of about 10–20% above maintenance and a gain of about 0.25–0.5% of body weight a week for beginners and intermediates, with advanced lifters going slower still. Muscle can only be built so fast; calories beyond what that growth needs are stored as fat.
A "dirty bulk" — eating everything in sight — reaches the scale weight faster, but much of it has to come off again in a cut. For most people, a lean or standard bulk wastes less time overall.
Most bulks fail on the days you undereat
Gain Weight is one of SlimAI’s three goals, with the same 250, 500 and 750 calorie surpluses as this calculator. Every meal you log counts toward the target, so a short day shows up before dinner rather than after a flat month.
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Your surplus has to move with you
Maintenance calories rise as you gain, because a heavier body costs more to run. A surplus worked out at 70 kg is smaller by the time you weigh 74.
Recalculate every 2–3 kg, or when your weekly average stalls for two weeks. If the scale is moving faster than the target rate, take 100–200 calories off; if it is not moving, add the same.
If you struggle to gain
Appetite, not knowledge, is the usual limit. Calorie-dense foods help: nuts, nut butters, olive oil, whole milk, dried fruit, rice and granola add calories without adding much volume.
Liquid calories are easier than solid ones. A milkshake of milk, oats, banana and peanut butter can be 600–800 calories that do not feel like a meal. Adding one extra meal or snack at a fixed time is easier than making every meal bigger.
Bulking Calories by Body Weight
Daily calories for a 25-year-old man, 178 cm (5 ft 10 in), moderately active. Your own figures will differ — the calculator above uses yours.
| Body weight | Maintenance | Lean bulk | Standard bulk | Aggressive bulk | Protein |
|---|---|---|---|---|---|
| 60 kg (132 lb) | 2,470 | 2,720 | 2,970 | 3,220 | 108 g |
| 70 kg (154 lb) | 2,620 | 2,870 | 3,120 | 3,370 | 126 g |
| 80 kg (176 lb) | 2,780 | 3,030 | 3,280 | 3,530 | 144 g |
| 90 kg (198 lb) | 2,930 | 3,180 | 3,430 | 3,680 | 162 g |
Maintenance by Mifflin-St Jeor × 1.55. Protein at 1.8 g per kg. A 25-year-old, 165 cm, 60 kg, moderately active woman has a maintenance of about 2,090 and a lean bulk of about 2,340.
How to Work Out Your Bulking Calories
Five steps, then two to three weeks of honest weigh-ins.
- 1
Find your maintenance calories
Basal metabolic rate × activity level. The TDEE calculator does this; so does the one above.
- 2
Add a surplus
+250 for a lean bulk, +500 for standard, +750 for aggressive. Underweight adults should not go below +500.
- 3
Set protein
1.6–2.2 g per kg of body weight. At 70 kg that is 112–154 g a day.
- 4
Set fat, then carbohydrate
Fat at about a quarter of calories, then carbohydrate for everything left. It fuels the training that makes the surplus worth it.
- 5
Check the rate
Weigh in daily, compare weekly averages. If you gain faster than 0.5% of body weight a week, trim the surplus.
The Formulas Behind This Calculator
Computed in your browser. Nothing is uploaded and nothing is stored between visits.
Maintenance
TDEE = BMR × activity factorBMR by Mifflin-St Jeor, or Katch-McArdle when you supply body fat. Activity factors from 1.2 to 1.9.
Surplus
surplus = min(choice, 1000, 0.5 × TDEE) · BMI < 18.5 → at least 500The same caps SlimAI applies to its Gain Weight goal.
Expected gain
kg per week ≈ surplus × 7 ÷ 7700A theoretical figure. Muscle and fat have different energy costs, so real gain varies.
Macros
protein = 1.8 g/kg · fat = 25% of kcal ÷ 9 · carbs = remaining kcal ÷ 4Protein within the 1.6–2.2 g/kg range; fat at a quarter of calories.
Sources and method
- Iraki J et al. (2019) — Sports (Basel) — Off-season nutrition review for natural bodybuilders: a surplus of about 10–20%, weight gain of about 0.25–0.5% of body weight a week for novice and intermediate lifters, protein 1.6–2.2 g/kg, fat 0.5–1.5 g/kg, and carbohydrate for the remaining calories.
- Morton RW et al. (2018) — systematic review and meta-analysis, British Journal of Sports Medicine — Protein supplementation increased resistance-training gains in lean mass, with the benefit plateauing at around 1.6 g/kg/day and a confidence interval extending to about 2.2 g/kg.
- Mifflin MD et al. (1990) — American Journal of Clinical Nutrition — The resting energy equation used for maintenance calories when body fat is not supplied, derived from 498 healthy adults.
FAQ
Still Wondering About SlimAI
How many calories do I need to bulk?
How many calories do I need to bulk?Your maintenance calories plus a surplus — 250 for a lean bulk, 500 for a standard bulk, 750 for an aggressive one. For a 70 kg, 178 cm, 25-year-old, moderately active man, that is about 2,870, 3,120 or 3,370 calories a day.
How fast should I gain weight on a bulk?
How fast should I gain weight on a bulk?About 0.25–0.5% of your body weight a week if you are a beginner or intermediate lifter, and slower if you are advanced. At 70 kg that is 0.18–0.35 kg (0.4–0.8 lb) a week. Faster than that, and more of the gain tends to be fat.
Is a lean bulk better than a dirty bulk?
Is a lean bulk better than a dirty bulk?For most people, yes. A smaller surplus builds close to the same muscle with far less fat, so the cut afterwards is shorter. A dirty bulk mainly suits people who are underweight or genuinely cannot gain on a moderate surplus.
How much protein do I need when bulking?
How much protein do I need when bulking?1.6–2.2 g per kg of body weight a day. At 70 kg that is 112–154 g. Beyond that, extra protein mostly displaces carbohydrate, which is better at fuelling the training that drives growth.
Do I need to bulk to build muscle?
Do I need to bulk to build muscle?Not always. Beginners and people returning to training can build muscle at maintenance or even in a small deficit, especially with high protein. A surplus makes it easier and faster, particularly for lean, experienced lifters.
Why am I not gaining weight on my bulk?
Why am I not gaining weight on my bulk?Usually because intake is lower than it feels, or activity is higher. Weigh food for a week, check your daily steps, and compare weekly average weights rather than single days. If nothing moves after two weeks, add 150–250 calories.
Can SlimAI help me gain weight?
Can SlimAI help me gain weight?Yes. Gain Weight is one of SlimAI’s three goals, with the same 250, 500 and 750 calorie surpluses used here, capped at 1,000 calories and half of maintenance. If your BMI is under 18.5 and you have no recorded medical condition, the surplus is at least 500. Your target is recalculated when your weight changes.
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