Calories: maintenance as the starting point
Whether you gain, lose or hold your weight is decided by energy balance. Your maintenance needs (TDEE) are made up of resting energy expenditure, digestion, training and everyday movement. Calculators usually estimate it with the formula by Mifflin and St Jeor (1990) and an activity factor.
This number is a good starting value, nothing more. Two people with identical data can differ clearly in their expenditure. Eat as consistently as possible for two to three weeks and compare your intake with your weight trend: if the trend stays flat, you have found your real maintenance.
Protein
Protein is the macro that matters most for muscle. The position stand of the International Society of Sports Nutrition (Jager and colleagues 2017) gives 1.4 to 2.0 g per kg of body weight per day for most people who train. Morton and colleagues (2018) found that the additional benefit for muscle gain levels off at about 1.6 g per kg. In a diet it can be more, because protein protects muscle and keeps you full.
Spread the amount across several meals. Schoenfeld and Aragon (2018) suggest about 0.4 g per kg of body weight per meal across at least four meals as a guideline. This is a practical aid, not a rigid rule: the daily amount matters more than the distribution.
Carbohydrates and fat
Once calories and protein are set, you split the rest between carbohydrates and fat. There is more leeway here than many diet camps claim. Carbohydrates fill the glycogen stores and support training with many sets. Fat is needed for hormone production and for absorbing fat-soluble vitamins.
For contest preparation, Helms and colleagues (2014) give 15 to 30 percent of calories from fat and the rest, after protein, from carbohydrates. Outside a hard diet, the split can be looser. The macro calculator divides your target calories accordingly.
What changes between bulk and cut
In a bulk you sit slightly above maintenance, in a cut below it. Protein stays high in both phases, and tends to be a bit higher in a cut. What mainly gets adjusted are carbohydrates and fat: in a bulk there is room for more carbohydrates around training, in a cut that room shrinks.
How big the surplus or deficit should be depends on the pace you want. The bulk and cut calorie calculator converts a target pace in percent of body weight per week into calories. Whether the number is right then shows in your weight trend.
Fiber, fruit and vegetables
Body composition is not everything. Fruit, vegetables, legumes and whole grains supply micronutrients and fiber, and they fill you up. The German Nutrition Society (DGE) recommends that adults eat at least 30 g of fiber per day. In a cut, bulky, high-fiber foods also help against hunger.
Consistency beats perfection
The best nutrition plan is the one you stick to for months. Recurring meals you like, a rough plan for restaurant visits and weekends, and honest logging of your calories bring more than a perfect plan that falls apart after two weeks.
Counting calories is a tool, not a must. Some people work with fixed portions and only look at the trend. What matters is that you notice when the trend drifts from your goal, and then adjust in a targeted way.
Supplements
Only a few supplements have solid research behind them. Best studied is creatine monohydrate, which can improve performance in short, intense efforts (ISSN position stand, Kreider and colleagues 2017). Because creatine draws water into the muscle, your weight often rises after you start; that is not fat. Protein powder is simply a convenient food.
Supplements replace neither your calorie target nor your protein target. If you have a medical condition or take medication, talk to a doctor before taking them.