Calories and macros: how to calculate your real daily needs
The full method to work out your basal metabolic rate, your daily expenditure and your macros — with the equations, a worked example, and what these numbers cannot tell you.
You type "how many calories per day" into Google, land on a calculator, and get a round number. Three weeks later, nothing has moved.
The problem is almost never the arithmetic. It is that you are handed a result without being shown where it comes from, or what it is worth. Here is the full method — the one dietitians use, and the one Coach Sport AI applies to build your diagnosis.
1. Your basal metabolic rate
Your basal metabolic rate is what your body burns at complete rest: breathing, holding your temperature, running your brain and organs. It is already the largest share of your daily expenditure.
The reference equation is Mifflin-St Jeor, published in 1990. It replaced the older Harris-Benedict formula because it is less wrong on modern populations.
For men:
BMR = (10 × W) + (6.25 × H) − (5 × A) + 5
W = weight in kg · H = height in cm · A = age
For women:
BMR = (10 × W) + (6.25 × H) − (5 × A) − 161
W = weight in kg · H = height in cm · A = age
The 166 kcal gap between the two is not about sex as such: it reflects an average difference in muscle mass and body composition. It is a statistical average, not a truth about you.
2. Your total daily expenditure
Your basal rate is not enough — you have to add everything you do during the day. So you multiply by an activity factor.
| Your daily life | Factor |
|---|---|
| Sedentary — desk job, little walking | 1.2 |
| Lightly active — 1 to 3 sessions a week | 1.375 |
| Moderately active — 3 to 5 sessions | 1.55 |
| Very active — 6+ sessions, or physical job | 1.725 |
Total expenditure = BMR × Factor
This is where most people get it wrong, and always in the same direction: upward. Three workouts a week does not make you "very active" if you spend the other six days sitting. When in doubt, pick the factor below.
3. Adjusting for your goal
Your total expenditure is your break-even point: eat that, and your weight holds. Then you shift it.
- Losing fat: around −400 kcal per day
- Building muscle: around +300 kcal per day
- Maintaining: no adjustment
- Performance: around +150 kcal per day
Why not −1000 kcal to go faster? Because a violent deficit costs you muscle alongside fat, wrecks your recovery, and does not survive three weeks. A moderate deficit takes off roughly 0.5 kg per week — slow on paper, and still there six months later.
4. Splitting protein, carbs and fat
Total calories decide whether you gain or lose. The split decides what you gain or lose: muscle or fat.
| Goal | Protein | Carbs | Fat |
|---|---|---|---|
| Fat loss | 35% | 35% | 30% |
| Muscle gain | 30% | 40% | 30% |
| Maintenance / performance | 25% | 45% | 30% |
In fat loss, protein goes up: that is what protects your muscle while you are in a deficit. In muscle gain, carbs go up, because they fuel your sessions.
To turn percentages into grams:
Protein : 1 g = 4 kcal
Carbs : 1 g = 4 kcal
Fat : 1 g = 9 kcal
5. A worked example
Take a 32-year-old woman, 168 cm, 68 kg, training three times a week, aiming to lose fat.
Basal metabolic rate
(10 × 68) + (6.25 × 168) − (5 × 32) − 161
= 680 + 1050 − 160 − 161
= 1409 kcal
Total expenditure — three sessions a week, so moderately active:
1409 × 1.55 = 2184 kcal
Target with a 400 kcal deficit:
2184 − 400 = 1784 kcal per day
Fat-loss split (35 / 35 / 30):
Protein : 1784 × 0.35 ÷ 4 = 156 g
Carbs : 1784 × 0.35 ÷ 4 = 156 g
Fat : 1784 × 0.30 ÷ 9 = 59 g
6. What this calculation does not know
Being honest about the limits matters, because nobody else tells you:
- It is an estimate. Two people with identical measurements can differ by 200 kcal. The formula gives a starting point, not a truth.
- It ignores body composition. At equal weight, a muscular person burns more. Mifflin-St Jeor does not measure that.
- It ignores your non-exercise activity. One factor, four steps: that is coarse. A job on your feet does not weigh like a desk job.
- Nothing replaces measuring. Hold your target for two or three weeks, weigh yourself under the same conditions, and adjust by 100 to 200 kcal based on what you see. Your body has the final word, not the formula.
Getting your numbers without doing the maths
You can work all of this out on paper with what is above — the whole method is here, nothing is hidden.
If you would rather go faster: Coach Sport AI applies these exact equations to your answers and hands you your basal rate, your estimated expenditure, your target and your macros. The diagnosis is free, no card required, and the assumptions behind the numbers are shown rather than hidden.
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