Fasting Window Calculator (Hours + Eating Window)

Use 24-hour format (HH:MM). For example, 8:00 PM is 20:00, and midnight is 00:00.

The calculator handles this automatically if you select "auto" mode. For example, if you start fasting at 20:00 and end at 12:00, it will calculate a 16-hour fast.

The schedule label shows a format like "16:8" meaning 16 hours fasting and 8 hours eating. It only appears if both durations are whole hours. Otherwise, it shows rounded hours with a "~" prefix.

Rounding rounds the fasting duration to the nearest 5 or 15 minutes. "Exact" keeps the precise calculation. Rounding only affects the fasting duration display, not the eating window calculation.

If start and end are the same time with "same day" mode, the fast is 0 hours (24-hour eating window). With "next day" mode, it's a 24-hour fast (0-hour eating window).

This is a time calculator that helps you understand your fasting and eating windows. Use it as a planning tool, but remember that individual needs vary and this is not medical advice.

No. This is an educational time calculator only. It calculates time durations and does not provide medical advice, recommendations, or guarantees about health outcomes.

Warnings appear for unusual durations (very short or very long fasts). Double-check your times if you see a warning, as it may indicate an input error.