How it works
The age we show isn't magic — it's a transparent reflection of the data you enter. Here's how it works.
Your data → a single, clear score
Which signals do we read?
Sleep
Duration and consistency are the foundation of recovery.
Energy
Your daytime energy level reflects your vitality.
Stress
Perceived stress load affects your balance.
Activity
Your movement and exercise logs.
Your age in three steps
You enter your data
Your profile (age, height, weight, goal) and daily check-in answers are the starting point. Everything is entered by you, as accurately as you know it.
We process it in the background
We weigh the signals you enter and compare them with your chronological age. No estimated device, sensor or lab data is used — only your own input.
You see your estimated age
The result is a single 'fjt age' estimate that reflects your habits. Watching it change over time keeps you motivated.
Important reminders
We're not doctors
fjt doesn't offer medical advice, diagnosis or treatment. Only make important health decisions — supplements, medication, nutrition — together with a physician. All we can do is reflect your own data back to you.
We don't give advice, the responsibility is yours
Activities exist only so you can keep a record; we never tell you what to do. All responsibility for using the app is yours.
Entirely your own data
The age shown isn't an externally measured value; it's an estimate calculated in the background purely from the data you entered. No data, no estimate.