Anyone who's spent time in a gym has encountered the cutting and bulking cycle. In theory, it's elegant: spend a period eating above maintenance to build muscle (bulk), then spend a period eating below maintenance to shed the fat accumulated alongside it (cut). Repeat until you achieve the physique you're after. In practice, most people either bulk too aggressively, accumulate far more fat than necessary, and then face a long and muscle-threatening cut — or cut too aggressively, lose significant muscle alongside the fat, and arrive at their goal looking smaller than they hoped.
The difference between effective and ineffective phases almost always comes down to the precision of the calorie targets.
Understanding TDEE as Your Baseline
Before setting cutting or bulking targets, you need an accurate Total Daily Energy Expenditure figure — the calories your body burns each day accounting for activity. TDEE is the baseline from which all adjustments are made. Eat at TDEE and your weight holds steady. Eat above it and you gain. Eat below it and you lose.
Use our calorie deficit calculator to calculate your TDEE based on weight, height, age, and activity level. Be honest about activity — it's the most commonly overestimated input, and an inflated TDEE leads to smaller than expected results in both directions.
Calculating Bulking Calories
The goal of a bulk is to provide enough of a calorie surplus to support muscle growth while minimising unnecessary fat gain. The rate of natural muscle growth is limited: drug-free beginners might gain 0.5-1kg of muscle per month in the first year; advanced lifters may gain 0.5-1kg in a year. These biological limits mean there's a ceiling to how much surplus is actually usable for muscle building.
A "lean bulk" — using a modest surplus of 200-300 calories above TDEE — maximises muscle gain relative to fat accumulation. A more aggressive surplus of 500+ calories per day produces faster scale weight gain, but a larger proportion of that gain will be fat tissue rather than muscle.
For most natural lifters, a 200-300 calorie surplus targeting 0.25-0.5kg of weight gain per week is the most efficient approach. Beginners can sustain slightly larger surpluses due to faster initial muscle gain rates.
Calculating Cutting Calories
A cut involves a calorie deficit to reduce fat mass while protecting muscle. The critical variable is adequate protein intake — without sufficient protein during a cut, muscle tissue becomes a fuel source alongside fat stores, and you lose strength and size you worked months or years to build.
A conservative deficit of 300-500 calories below TDEE, paired with protein intake at 2-2.4g per kg of bodyweight, minimises muscle loss during a cut. More aggressive deficits accelerate fat loss but increase muscle catabolism risk, especially as the cut progresses and body fat percentage drops.
Our macro calculator generates protein, fat, and carbohydrate targets for both cutting and bulking phases. For a cut, prioritise hitting the protein target above all other macros — carbs and fats fill the remaining calorie budget according to personal preference and training requirements.
Protein: Non-Negotiable in Both Phases
During a bulk, protein supports muscle protein synthesis — the process by which the body builds new muscle tissue from the training stimulus. During a cut, protein protects existing muscle against breakdown in a calorie-deficit environment. In both phases, the target is broadly similar: 1.6-2.4g of protein per kg of bodyweight per day.
The lower end of that range is typically sufficient for intermediate lifters in a modest surplus. The higher end is appropriate for aggressive cuts, very lean individuals, or advanced trainees with significant muscle mass to protect.
How Long Should Each Phase Last?
Phase duration depends on your starting body composition and goals. General guidelines:
A bulk is most effective when started from a relatively lean base — roughly 12-15% body fat for men, 22-25% for women. Starting a bulk with high body fat produces less favourable muscle-to-fat gain ratios and results in a much longer subsequent cut. End a bulk when body fat has increased to around 18-20% (men) or 28-30% (women).
A cut continues until a leaner target is reached — typically 10-14% for men or 18-22% for women for most recreational goals, allowing room for a subsequent lean bulk. Cuts lasting longer than 16-20 weeks at moderate deficits can increase metabolic adaptation; a brief maintenance phase ("diet break") can reset metabolic rate before continuing.
Body Recomposition: An Alternative
For beginners and detrained individuals returning to training, simultaneous fat loss and muscle gain — body recomposition — is achievable. Eating at or slightly below maintenance with high protein intake allows muscle to be built from training stimulus while body fat is simultaneously reduced. This becomes increasingly difficult for advanced trainees with higher muscle mass and lower body fat.
The NHS guidance on exercise for health provides helpful context on training alongside nutrition for anyone new to structured fitness goals.
Tracking Progress Properly
During a bulk, scale weight alone is misleading — water, glycogen, and food weight all fluctuate daily. Track a 7-day rolling average and trend over weeks. During a cut, the same principle applies: water retention from training stress can temporarily mask fat loss. Take body measurements and progress photos alongside scale weight for a complete picture of what's actually changing.