Calorie calculator - daily calorie need

Three examples with different people

The figures are calculated exactly as the calculator shows them. Compare how much the result depends on age, sex and above all activity level.

• Man, 40, 182 cm, 85 kg, moderate activity: BMR 1793 kcal, daily need 2779 kcal, mild weight loss 2529 kcal, weight loss 2279 kcal, muscle gain 3079 kcal.
• Woman, 25, 168 cm, 58 kg, active: BMR 1344 kcal, daily need 2318 kcal, weight loss 1818 kcal.
• Woman, 55, 163 cm, 64 kg, sedentary: BMR 1223 kcal, daily need 1468 kcal, and 1223 kcal in both the mild weight loss and weight loss rows.

Why the weight loss row can equal your BMR

The calculator never suggests eating below your basal metabolic rate. In the third example 1468 - 500 = 968 kcal, which is well below the BMR of 1223 kcal, so the calculator shows 1223 kcal. The real deficit is then only 245 kcal a day, and weight comes off at closer to 0.25 kg per week.

With a sedentary lifestyle this almost always happens, because the daily need is only 20% above BMR. At light activity it affects people with smaller bodies: the same woman with light activity would get a daily need of 1682 kcal, yet the weight loss row would still sit at 1223 kcal. In that situation adding movement, which raises daily expenditure, works better than cutting food further.

Choosing the activity level is the biggest source of error

The man in the first example would get a daily need of 2152 kcal if sedentary and 2779 kcal at moderate activity. That 627 kcal gap is larger than the whole recommended weight loss deficit. Pick a level that is too high and you can eat "in a deficit" without losing weight.

The factors are: sedentary 1.2, light 1.375, moderate 1.55, active 1.725, very active 1.9. An office worker who trains for an hour three times a week usually fits light better than moderate. Very active is meant for people with a physical job plus regular training. When in doubt, pick the lower level and adjust based on results.

The result changes as you do

If the man in the first example goes from 85 kg to 77 kg, his BMR falls to 1713 kcal and his daily need to 2655 kcal, a drop of 124 kcal. If he keeps eating the same amount, his deficit shrinks and weight loss slows. Recalculate after every 4-5 kg lost.

Age matters too: each year lowers BMR by 5 kcal in the formula. A 25-year-old man with the same body would get a BMR of 1868 kcal and a daily need of 2895 kcal, 116 kcal more than at 40. For the same weight, height and age, the male and female formulas always differ by 166 kcal of BMR.

How to check the number against your own weight

The Mifflin-St Jeor equation estimates most people's needs to within about 10%, but individual metabolism can differ. The most reliable test is your own weight: eat according to the calculator for 2-3 weeks, weigh yourself under the same conditions several times a week and compare weekly averages.

As a rule of thumb, a kilogram of body fat corresponds to about 7700 kcal, so a daily deficit of 500 kcal gives roughly 0.45 kg per week. If your average weight does not move in the expected direction, change your daily intake by 100-200 kcal. Bear in mind that counting by eye without weighing food usually misses some calories.

The formula is not suitable during pregnancy or breastfeeding, for under-18s or for people with eating disorders. If you have diabetes, kidney disease or another chronic condition, or take medicines that affect blood sugar, agree on a suitable energy intake with your doctor or a dietitian.