Work out a daily calorie surplus for bulking, your expected weekly weight gain, and an estimated date to reach your goal weight — based on the Mifflin-St Jeor formula.
A calorie surplus means eating more calories than your body burns in a day (your TDEE, or Total Daily Energy Expenditure). This calculator estimates your TDEE from your BMR and activity level, then adds a percentage on top — 10%, 15%, 20% or 25% — to give you a daily calorie target for gaining weight. Combined with resistance training and enough protein, that extra energy gives your body the raw material to build new muscle tissue, not just add fat.
| Surplus level | Target kcal/day | Daily surplus | Est. weekly gain |
|---|
A calorie surplus calculation starts from the same BMR and TDEE foundation as a deficit, then adds a percentage instead of subtracting one.
Using a fixed reference person — a 25-year-old man, 175 cm, moderately active — here's how a 15% surplus target scales with starting body weight. Your own number will differ with your age, height, sex and activity level; use the calculator above for your figures.
| Body weight | BMR | TDEE | Target (15% surplus) |
|---|---|---|---|
| 60 kg | 1,574 kcal | 2,440 kcal | 2,806 kcal/day |
| 70 kg | 1,674 kcal | 2,595 kcal | 2,984 kcal/day |
| 80 kg | 1,774 kcal | 2,750 kcal | 3,163 kcal/day |
| 90 kg | 1,874 kcal | 2,905 kcal | 3,341 kcal/day |
| 100 kg | 1,974 kcal | 3,060 kcal | 3,519 kcal/day |
Whatever combination of foods gets you there, the size of your daily surplus is what drives your rate of scale-weight gain. Using the same 7,700 kcal-per-kilogram approximation used elsewhere on this site:
| Daily surplus | Estimated weekly gain |
|---|---|
| 200 kcal/day | 0.18 kg/week |
| 300 kcal/day | 0.27 kg/week |
| 400 kcal/day | 0.36 kg/week |
| 500 kcal/day | 0.45 kg/week |
| 600 kcal/day | 0.55 kg/week |
| 750 kcal/day | 0.68 kg/week |
Worth being upfront about: the 7,700 kcal/kg figure was originally calibrated to fat tissue, not muscle. In a surplus, the weight you gain on the scale is a mix of muscle and fat, and the split depends heavily on your training and protein intake — so treat these numbers as a rough estimate of total scale-weight change, not a promise of how much muscle you'll actually build.
A "dirty bulk" pushes calories way above maintenance on the theory that more food equals more muscle. It doesn't really work that way. Muscle protein synthesis has a ceiling — your body can only build new tissue so fast, even with unlimited food and a genetics lottery win. Once you're eating well past what your training and recovery can use, the extra energy is stored as fat, not muscle, and the fat tends to arrive faster than the muscle does. A "lean bulk" keeps the surplus modest — generally in the 10–20% range covered by this calculator — which is enough to fuel muscle growth without opening the floodgates to unnecessary fat gain. Two things matter more than the surplus size itself: resistance training that progressively challenges your muscles (without it, a surplus mostly just adds fat), and enough dietary protein to give your body the building blocks it needs. Get those two right and a smaller surplus produces a noticeably better ratio of muscle to fat than an aggressive one does.
There's no single "correct" surplus — it depends on your training experience, how fast you want to gain, and how much fat gain you're willing to accept along the way. A 10% surplus is a conservative, "lean bulk" style approach that suits people who are already fairly lean and want to keep it that way while adding muscle slowly. A 15% surplus is a common middle-ground choice, giving your body clearly enough fuel to build muscle without piling on excess fat too quickly. A 20% surplus speeds up the scale, which can suit newer lifters whose bodies are especially responsive to training, but it also means a bigger share of that gain risks being fat. A 25% surplus is really only worth considering for a short, deliberate phase — most people find that anything beyond it mostly just adds body fat rather than extra muscle, since your body can't build tissue any faster no matter how much food you throw at it.
| Surplus | Typical use case | Trade-off |
|---|---|---|
| Lean / mini bulk — 10% | Staying lean while slowly adding muscle | Slower gains, but the cleanest muscle-to-fat ratio |
| Moderate bulk — 15% | Most people's default bulking target | Solid muscle-building fuel without excess fat gain |
| Standard bulk — 20% | Newer lifters chasing faster visible gains | Quicker scale progress, more fat comes along for the ride |
| Aggressive bulk — 25% | Short, deliberate mass-gain phases | Fastest weight gain, but the least efficient for muscle specifically |
Your BMR is the energy your body burns at complete rest. Your TDEE multiplies that by an activity factor to estimate your full daily burn — this is your maintenance level, the calories that keep your weight stable. Your target daily calories is TDEE plus your chosen surplus percentage. The weekly gain estimate converts your daily surplus into an expected rate of scale-weight increase using the standard energy-density approximation, and the goal date projects that rate forward from today to your goal weight. None of this tells you exactly how much of that gain will be muscle versus fat — that's determined by your training program and protein intake, not the calculator.
How many calories should I eat to build muscle?
Start from your TDEE (maintenance calories) and add a surplus of 10–20%. For a 70kg moderately active man with a TDEE of about 2,556 kcal, a 15% surplus works out to around 2,939 kcal a day — an extra 383 kcal above maintenance. The right number for you depends on your own weight, height, age and activity level, which is what the calculator above works out.
What is a good calorie surplus for lean bulking?
Most people aiming for a lean bulk do well with a 10–15% surplus above TDEE. That's enough extra energy to support noticeable muscle growth when paired with resistance training and sufficient protein, without adding fat as quickly as a bigger surplus would. Surpluses above 20% tend to add weight faster but with a worse split between muscle and fat.
How much weight will I gain in a calorie surplus?
Using our worked example — a 70kg, 30-year-old, 175cm man at moderate activity with a 15% surplus — the daily surplus is about 383 kcal, which works out to roughly 0.35 kg of scale weight gained per week. Gaining 5kg at that rate takes about 14.4 weeks, a little over three months. A bigger surplus speeds up the number on the scale but doesn't necessarily speed up muscle growth by the same amount.
Will I gain fat in a calorie surplus?
Almost certainly some, yes — very few people add muscle with zero fat gain while eating above maintenance. The question is really about ratio, not whether it happens at all. A smaller, well-managed surplus combined with resistance training and good protein intake tends to produce mostly muscle with a modest amount of fat, while a very large surplus shifts that ratio heavily toward fat.
What's the difference between a lean bulk and a dirty bulk?
A lean bulk uses a modest surplus, typically 10–20% above TDEE, aiming to gain muscle with as little added fat as possible. A dirty bulk uses a much larger surplus with less attention to food quality or portion control, gaining weight faster but with a much larger share of that gain being fat. Since muscle can only be built so quickly regardless of how much you eat, a dirty bulk mostly just means more fat to lose later.
How much protein do I need in a calorie surplus?
Protein is what actually gets used to repair and build muscle tissue — the calorie surplus just supplies the energy to support that process. Sports nutrition guidance in Australia generally points toward higher protein intakes for people doing regular resistance training than for a sedentary person, spread fairly evenly across meals. For specific targets suited to your body weight and training, see our Protein Calculator or check with an accredited sports dietitian.
Do I need to be in a calorie surplus to build any muscle at all?
Not always — some muscle gain is possible at maintenance calories or even in a mild deficit, particularly for beginners or people returning to training after time off. But a surplus makes the process more efficient and reliable, giving your body a consistent buffer of extra energy to draw on for recovery and growth, which is why most structured bulking phases use one.
How long should I bulk for?
There's no fixed answer, but many lifters run a bulking phase for a few months up to around six months, then reassess based on how their physique and strength have progressed. Longer bulks with a small surplus tend to keep fat gain more manageable than trying to gain a large amount of weight quickly. Some people prefer shorter, more controlled phases followed by a brief maintenance or cutting period to keep body composition in check.