How many calories do you need? The formula, worked out
The Mifflin-St Jeor formula worked out for two real examples, with activity factors, fat loss and muscle gain adjustments, and how to turn it into meals.
Key takeaways
- BMR = 10 × kg + 6.25 × cm − 5 × age, plus 5 for men or minus 161 for women, then multiply by your activity factor.
- Subtract about 400 kcal for fat loss or add about 250 kcal for muscle gain; set protein at 2 g per kg.
- The formula has a 10% error band, so adjust by 150 kcal after two weeks of weekly weight averages.
Most calorie targets you see online are guesses dressed up as rules. 1,200 for women, 1,800 for men, eat less than you burn. None of that tells you what you specifically need. There is a formula that does a decent job, it fits on one line, and you can work it out on your phone calculator in under a minute.
The Mifflin-St Jeor formula
This is the equation most dietitians use to estimate your basal metabolic rate, the calories your body burns at complete rest in a day.
- Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
- Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
That number is your BMR. It is what you would burn lying in bed all day. Nobody does that, so the next step multiplies it by an activity factor.
| Your week | Multiply BMR by |
|---|---|
| Desk job, no exercise | 1.2 |
| Desk job, gym 3 to 4 days | 1.375 |
| Gym 5 to 6 days, or an active job | 1.55 |
| Physical job plus daily training | 1.725 |
Most people reading this are in the 1.375 row. Be honest. Three hours a week in the gym plus sitting the rest of the time is light activity, not moderate, however hard the workouts feel.
Worked example: Rahul, 26, 70 kg, 172 cm
Rahul works in IT in Pune, trains four days a week and wants to lose fat.
- BMR = (10 × 70) + (6.25 × 172) − (5 × 26) + 5 = 700 + 1,075 − 130 + 5 = 1,650 kcal
- Maintenance = 1,650 × 1.375 = 2,270 kcal
- Fat loss target = 2,270 − 400 = 1,870 kcal
- Protein target = 70 × 2 = 140 g
So Rahul eats about 1,870 kcal a day with 140 g protein. At a 400 kcal daily deficit he should lose roughly 0.4 kg a week, which is a sensible pace that keeps his lifts going.
Worked example: Priya, 28, 62 kg, 162 cm
Priya is a teacher in Ahmedabad, does gym three days a week and wants to build some muscle while staying about the same weight.
- BMR = (10 × 62) + (6.25 × 162) − (5 × 28) − 161 = 620 + 1,012 − 140 − 161 = 1,331 kcal
- Maintenance = 1,331 × 1.375 = 1,830 kcal
- Muscle gain target = 1,830 + 250 = 2,080 kcal
- Protein target = 62 × 2 = 124 g
Notice the gap between them. Priya's muscle gain target is only 200 kcal above Rahul's fat loss target. Body size, sex and age move the number a lot, which is exactly why copying a friend's diet plan rarely works.
Why −400 and +250, not bigger numbers
A 400 kcal deficit is enough to lose 1.5 to 2 kg a month without feeling starved or losing strength. Go to 800 and you will lose faster for two weeks, then start skipping workouts and eating a whole packet of Parle-G at 11 pm. Smaller and steady beats a crash.
For muscle gain, your body can only build so much tissue per week. A beginner might add 1 kg of muscle a month at best. 250 extra kcal supports that. 700 extra mostly becomes fat you will have to lose later.
Repyra uses this same formula and the same −400 and +250 adjustments when it sets your targets, so if you have the app, the maths is already done and recalculated when your weight changes.
What the formula gets wrong
It is an estimate with roughly a 10% error band. Two people with the same stats can differ by 200 kcal a day because of muscle mass, genetics and how much they fidget.
So treat your first number as a starting point, not a verdict. Eat at the target for two weeks, weigh yourself every morning after the toilet and before breakfast, and compare weekly averages. If the average has not moved on a fat loss plan, cut 150 kcal. If you are gaining more than 0.5 kg a week on a muscle plan, cut 150 kcal. Adjust in small steps, not large ones.
Daily weight swings of a kilo are normal and mean nothing. Salt, a big dinner, your period, a long bus ride. Only the weekly average counts.
Turning the number into food
Rahul's 1,870 kcal with 140 g protein looks like this: 3 eggs and 2 rotis at breakfast (450 kcal, 24 g), 100 g cooked chicken with 1 cup rice and salad at lunch (420 kcal, 35 g), 200 ml milk and a fistful of peanuts in the evening (285 kcal, 14 g), and 50 g dry soya chunks as sabzi with 2 rotis and curd at dinner (545 kcal, 35 g). That is about 1,700 kcal and 108 g, leaving room for a scoop of whey or 100 g paneer to close both gaps.
If you are under 18, pregnant, or managing a medical condition, get the target from a doctor or dietitian rather than this formula.
Questions people ask
Which activity factor should I pick if I go to the gym four days a week?
If you sit for work the rest of the day, use 1.375. Most people overestimate their activity, and picking 1.55 for a desk job plus gym leads to a target that is 200 to 300 kcal too high.
Why is my fat loss target so low as a woman?
Smaller bodies burn fewer calories at rest, so the formula gives lower numbers. If your fat loss target falls below about 1,300 kcal, use a smaller deficit of 250 kcal and add activity instead.
How often should I recalculate?
Every 3 to 4 kg of weight change, or whenever your training schedule changes. Between recalculations, adjust by 150 kcal based on your weekly weight average.
