How your calorie needs are worked out
First, what your body burns at rest is worked out with the Mifflin-St Jeor formula: 10 × weight in kilos + 6.25 × height in centimetres − 5 × age, plus 5 for men and minus 161 for women. A man of 80 kg, 180 cm and 30 years burns about 1,780 kcal at rest.
That number is then multiplied by your activity level: 1.2 for sedentary, 1.375 for lightly active, 1.55 for moderately active and 1.725 for very active. The answer is your maintenance, roughly what you can eat without your weight changing. Count your training when you choose a level. If you train several days a week, you are usually one step above your everyday life.
Your goal
To lose weight, the calculator uses 80 percent of your maintenance, or 75 percent if your BMI is over 30. To build muscle, it adds 10 percent. Keeping your weight is your maintenance, rounded. These are the same rules BIP uses when a programme works out your diet.
The macros
Protein is worked out per kilo of body weight: 2 grams per kilo when you want to lose weight or build muscle, and 1.8 grams when you want to keep your weight. Fat is 0.8 to 1 gram per kilo. The rest of the calories become carbs. A gram of protein or carbs gives 4 kcal and a gram of fat 9 kcal, so the macros add up to the daily target.
Plenty of protein helps you keep your muscle when you eat less, and build new muscle when you eat more. It works best together with strength training, such as one of the training programmes.
An estimate, not the final answer
The formula is often within about ten percent, but it does not know your body. Eat to the number for two to three weeks and follow your weight. If it stands still when you want it to drop, or does not move when you want it to rise, change by 100 to 200 kcal a day and wait again.
The calculator is for adults. If you are under 18, pregnant, breastfeeding or have an eating disorder, other advice applies, and you should talk to a doctor or dietitian instead.
Let BIP do the work
When you create a programme in BIP, your calorie needs and macros are worked out with the same formula, together with a training programme for your goal. Create your programme and get both the training and the numbers in one place.