How your calorie and protein targets are worked out

Homekcal asks a few questions when you start: your goal, sex, age, height, weight and how active you are. From those it suggests a daily calorie target and a daily protein target. The app shows how each one was worked out, and you can change either at any time. This page is the same explanation in full.

Step 1: energy at rest

Resting energy is estimated with the Mifflin-St Jeor equation, published in 1990 and widely used in clinical nutrition:

• Men: 10 × weight in kg + 6.25 × height in cm − 5 × age in years + 5
• Women: 10 × weight in kg + 6.25 × height in cm − 5 × age in years − 161
• If you choose another option or prefer not to say, the last term is the midpoint of the two, − 78.

Step 2: how active you are

Resting energy is multiplied by an activity factor: 1.2 for mostly sitting, 1.375 for light activity, 1.55 for moderate activity, 1.725 for active, 1.9 for very active. The result is an estimate of the energy you use in a day.

Step 3: the goal

• Maintain: the target is the estimate from step 2.
• Lose weight: the target is 500 kcal a day below the estimate. A bigger gap is harder to keep up and harder on muscle.
• More protein: calories stay at maintenance and the protein target goes up.

Targets are rounded to the nearest 10 kcal.

Step 4: protein

Protein is set from body weight: 1.2 g per kg when the goal is losing weight, 1 g per kg to maintain and 1.6 g per kg when the goal is more protein. If your BMI is above 30, protein is worked out from an adjusted weight instead of your full weight: the weight you would be at a BMI of 25, plus 40 percent of the difference. That keeps the target realistic.

The floors

A suggested target never goes below 1,200 kcal a day for women or 1,500 kcal a day for men and everyone else, and if you type your own target below the floor, it is raised to the floor. For comparison, the US National Heart, Lung, and Blood Institute's practical guide describes 1,000 to 1,200 kcal a day for most women and 1,200 to 1,600 kcal a day for men as weight loss diets.

If the weight you enter puts your BMI under 18.5, Homekcal does not suggest a deficit at all. Days logged well under the floor never get praise or a streak glow, and if that keeps happening the app shows one calm message with places to get support.

A worked example

A woman aged 35, 160 cm tall, 70 kg, lightly active, who wants to lose weight:

1. Resting energy: 10 × 70 + 6.25 × 160 − 5 × 35 − 161 = 1,364 kcal
2. Daily estimate: 1,364 × 1.375 = about 1,876 kcal
3. Goal: 1,876 − 500, rounded, is 1,380 kcal, which is above her 1,200 floor, so it stands.
4. Protein: her BMI is about 27.3, so her full weight is used: 1.2 × 70 = 84 g a day.

What these targets are not

They are estimates from an equation, not a measurement of your body and not medical advice. Equations like this can be off by a few hundred calories for a given person. If your weight does not move the way you expect over a few weeks, adjust the target. If you are pregnant, breastfeeding, have a medical condition or take medicine that affects appetite or weight, talk to a doctor or dietitian before following any target. Homekcal is for adults aged 18 and over.