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.
Try it with your own numbers
Your result
Maintenance, no deficit or surplus applied
10 x 82.0 + 6.25 x 178.0 - 5 x 30 + 5 = 1787.5 kcal
Maintenance
1787.5 x 1.55 = 2,770 kcal (rounded to the nearest 10)
The rest of this page explains every step of that calculation. If you only want the number, the calorie calculator is the same tool on its own page.
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.
Trace a target through the Phasebuilt builder
Consider a constructed example: a 30-year-old man weighing 75 kg at 175 cm, selecting an activity multiplier of 1.55. The resting-energy calculation is 10 × 75 + 6.25 × 175 − 5 × 30 + 5 = 1,698.75 kcal. Multiplying by 1.55 gives 2,633.06 kcal, which the detailed builder rounds to 2,630.
For the steady fat-loss option, the builder subtracts 375 kcal, producing 2,255 kcal. If the intake reports under six hours of sleep or high stress, it adds 100 kcal back, producing 2,355. These pace and recovery adjustments are Phasebuilt's planning rules, not part of the original Mifflin equation and not clinically validated thresholds.
Why the calculator and plan may differ
A maintenance calculator estimates energy use. The builder also applies your goal, selected pace and recovery answers. Compare identical inputs and distinguish maintenance from a goal target. The detailed plan uses 1.8 g protein per kg for general fitness or fat loss and 2 g per kg for muscle building, with fat set at 0.8 g per kg. Carbohydrate is calculated from the remaining energy. The engine withholds the result when less than 80 g remains rather than raising carbohydrate above the calculated remainder. Rounded macro energy may differ by up to 2 kcal; these remain educational estimates, not clinical meal prescriptions.
Check the estimate against ordinary life
A training session does not make an otherwise seated day highly active. Start with the activity option that describes your whole week. If weighing yourself is appropriate for you, compare averages taken under similar conditions over several weeks, alongside energy, hunger and training performance. An isolated increase after a salty meal or hard session does not establish fat gain. If the estimate does not fit your trend, reassess your inputs and portion estimates before repeatedly reducing food.
Evidence and scope
These are educational examples for healthy adults, not individual prescriptions. The examples are constructed to explain decisions, not reports of user results. Phasebuilt publishes this guidance; no clinical review is claimed. See our method and limitations and report a correction.
- Mifflin et al.: the original resting-energy prediction equation
- ISSN position stand: protein and exercise
Updated 5 October 2026. Examples and implementation notes by Phasebuilt.
Get this calculated for your own measurements in about a minute.
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