Where does my daily target come from?

The Mifflin-St Jeor equation, applied to your sex, age, height, weight, goal and chosen pace — and the app shows its working, so you can see your BMR, your TDEE and the daily deficit rather than just a number. From there it adapts to the energy balance your own logs and weigh-ins actually show, and it asks before it moves. Prefer your own number? Set a custom target in Settings → Goal & Body Stats and Gretl will track against that instead, though never below a safe floor.