Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — the energy cost of simply being alive. Breathing, circulation, cell repair, temperature regulation — none of it is free. Your BMR is what all of that costs before you move a muscle.
AlterMe calculates your BMR using the Mifflin-St Jeor equation, a clinically validated formula based on four inputs: your weight, height, age, and biological sex. Each one matters — more body mass requires more energy to maintain, metabolism naturally slows with age, and men and women have different body composition patterns that affect energy needs.
Why it matters for your calorie target
Your BMR is the floor your calorie plan is built on. AlterMe will never set a deficit that cuts into it. No matter how aggressive your goal pace, your body always gets what it needs to function. Your deficit is drawn entirely from your active calories — the energy produced by movement — not from the calories keeping your organs running.
Why it changes over time
As you lose weight, your BMR decreases — a smaller body simply costs less to maintain. This is why your calorie target adjusts week to week rather than staying fixed. It is not a glitch. It is the plan adapting to your current body, not your starting one.
For more on how that works, see: Why does my calorie target change week to week?
BMR doesn't tell the full picture
Your BMR is the starting point, not the answer. On its own it only accounts for what your body burns at rest — it says nothing about how active you are, what your goals are, or how your body is changing over time. Two people with identical BMRs can have very different calorie targets depending on how much they move, how aggressively they want to progress, and what their body composition looks like. BMR is the foundation. Everything built on top of it is what makes your plan yours.