BeslyHow Besly calculates your calorie target
Every calorie app gives you a number on day one. Very few tell you where it came from. Here is ours, start to finish.
1. Your basal rate
We start with the Mifflin-St Jeor equation, the formula most dietitians reach for and the one validated as the most accurate of the common predictive equations for healthy adults. It uses weight, height, age and sex to estimate the energy your body burns at complete rest.
Older apps sometimes use Harris-Benedict (1919, revised 1984) or Katch-McArdle (which needs a body-fat percentage most people don't have). We tested all three and kept one: offering a menu of equations gives the illusion of precision without adding accuracy.
2. Your activity factor
Resting energy is only part of the day. We multiply it by an activity factor — sedentary through athlete — to get your maintenance level, the amount that keeps your weight where it is.
If you connect Apple Health, that multiplier stops being a guess: your actual steps and workouts are read each day and the target follows them.
3. Your deficit (or surplus)
Then comes the only part you choose: pace. Roughly 7,700 kcal separates you from a kilogram of body weight, so a 0.5 kg per week goal implies about a 550 kcal daily deficit. Besly shows this number openly on the goal screen — the deficit, not just the total.
We clamp the result at a floor. If your maths lands below the minimum considered safe for your body, Besly raises the target and tells you why. A number that starves you is not a plan.
4. Why the target moves during the day
Because you do. Walk 12,000 steps and the energy you burned is added; do a strength session and the same applies. This is why your remaining calories can go up in the afternoon — you earned it.
5. What it is not
An estimate. Predictive equations carry an error margin of roughly ±10% for most people and more for outliers. Body composition, medication, thyroid function and sleep all move the real number. Use it as a starting line and let the scale trend over two to three weeks tell you whether it needs adjusting — which is exactly what the coach watches for you.