End of fasting calculator

When to break your fast

The end of your fasting window is the moment your fast duration elapses from the start time. For a 16-hour fast starting at 8:00 PM, the eating window opens at 12:00 PM the next day.

Breaking a fast gradually is advisable for longer fasts (24+ hours): start with something light and easy to digest — fruit, broth, or yoghurt — before moving to a full meal. For standard 16:8 or 18:6 fasts, normal meals are fine.

What counts as "fast start"?

Your fast starts the moment you finish your last caloric intake — not when you decide to start fasting. If your last meal ended at 7:45 PM, that's your start time, not 8:00 PM. For precision, enter the actual time you finished eating.

Stages of fasting

• 0–4 hours — Fed state: insulin elevated, digestion active
• 4–12 hours — Post-absorptive state: glycogen being used, insulin falling
• 12–16 hours — Early fasting: liver glycogen depleted, fat burning begins
• 16–24 hours — Fasting state: ketosis beginning, autophagy increasing
• 24–72 hours — Extended fast: deep ketosis, significant autophagy

Track your fast in Left

Add your fast end time as a countdown in Left. Pin the widget to your Lock Screen and you'll always know exactly how long until you can eat — without mental arithmetic or checking a separate app.