This free quiz starts with a few safety screening questions, then matches you to one of five starting windows, 12:12, 14:10, 16:8, 18:6, or 20:4, based on your current habits and goals. It takes about two minutes. It's general information, not medical advice; talk to your doctor before changing how or when you eat.

Already know your window? Try the free Fasting Companion Tracker to time it and keep a private, on-device history.