How many calories
do I need?
There is no single number that applies to everyone, which is why this question is usually answered badly. It depends on your size, age, sex, how much you move and what you are trying to do. Here is the whole calculation, so you can do it yourself or check what any calculator tells you.
Step 1. Resting metabolism
Start with resting energy expenditure, the energy your body uses at complete rest. The most widely used estimate in clinical practice is the Mifflin St Jeor equation, published in 1990:
(10 × weight in kg) + (6.25 × height in cm) − (5 × age in years)
then +5 for men, or −161 for women
Source: Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition 1990;51(2):241 to 247.
Step 2. Multiply by how much you move
Resting metabolism only describes you lying still. Multiply it by an activity factor to estimate a whole day:
- Mostly seated
- × 1.2
- Lightly active
- × 1.375
- Moderately active
- × 1.55
- Very active
- × 1.725
That result is your maintenance level: roughly what holds your weight steady.
Step 3. Adjust for your goal
Fat loss means eating below maintenance, building muscle means slightly above. Size the change to something you can sustain, because the aggressive version is the one people abandon.
- Fat loss, gentle
- 250 below maintenance
- Fat loss, steady
- 375 below maintenance
- Fat loss, ambitious
- 500 below maintenance
- Muscle gain, gentle
- 150 above maintenance
- Muscle gain, steady
- 225 above maintenance
- Muscle gain, ambitious
- 325 above maintenance
Step 4. Account for recovery
Phasebuilt reduces a fat loss deficit by 100 calories if you report under six hours of sleep or high stress. A large deficit stacked on poor recovery tends to cost training quality and lean mass rather than speed anything up.
A full worked example
A 34 year old man, 178 cm, 82 kg, moderately active, fat loss at a steady pace:
- Resting metabolism
- (10 × 82) + (6.25 × 178) − (5 × 34) + 5 = 1,768
- Maintenance
- 1,768 × 1.55 = 2,740
- Daily target
- 2,740 − 375 = 2,365 calories
With under six hours of sleep reported, the safeguard lifts that to 2,465.
Then what about protein, carbs and fat?
Protein is set first, then fat, and carbohydrate fills the remainder. For the same person that works out at 148 g protein, 66 g fat and 295 g carbohydrate. See how much protein you need for why protein comes first.
Treat the number as a starting point
Predictive equations estimate a population average, not you specifically. Individual metabolism varies around the prediction. What matters is the following two to three weeks: if weight and performance are not moving as expected, adjust. No equation removes that step, and being roughly right and consistent beats being precisely wrong.
Get this calculated for your own measurements in about a minute.
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