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16:8 Fasting Schedule Calculator

Set up your 16:8 fasting schedule in seconds.

How it is calculated

The only input is the hour of your first meal on a 24-hour clock, and it can be decimal: 11.5 means 11:30. The schedule is fixed at an 8-hour eating window. eating start = first meal hour, eating end = first meal hour + 8 (wrapped to 0 to 24), the fast begins when eating ends, and it ends when eating starts again, which is 16 hours later. Times are shown as hh:mm, with minutes rounded. The hour must be from 0 to 23.99; 24 or a negative number gives no result. If the window crosses midnight, the end time is early the next morning. You cannot change the 16:8 ratio here, and the tool does not say whether this pattern is suitable for you.

Worked example

Your first meal is at 11.5, which is 11:30. The eating window starts at 11:30. Eating ends at 11.5 + 8 = 19.5, which is 19:30. The 16-hour fast starts at 19:30 and ends at 11:30 the next day. Had the first meal been at 20, the 8 hours would cross midnight, so eating would end at 04:00 and the fast would run from 04:00 until 20:00.

Try this example →

Common mistakes

  • Typing the clock time as 11:30 or 11.30. The field takes a decimal hour, so half past eleven is 11.5 and 11.30 would mean 11:18.
  • Entering the time of the last meal rather than the first. The tool counts forward 8 hours from the value, so a last meal time of 20 gives eating until 04:00.
  • Entering 24 for midnight. The accepted range is 0 to 23.99, so use 0.
  • Looking for a different fasting ratio. This tool is fixed at 16:8; for 18:6 or 20:4 a tool that takes the fasting length is needed.
  • Reading an end time such as 02:00 as earlier on the same day. If the window starts late in the evening, it ends in the early hours of the next day.

Sources

About this calculator

16:8 time-restricted eating compresses all daily calorie intake into an 8-hour window and fasts for the remaining 16 hours, making it the most widely studied schedule in the broader intermittent-fasting family that also includes 5:2 and alternate-day fasting. The approach was popularized by Martin Berkhan's “Leangains” protocol and has since been examined in circadian-biology research, including time-restricted-eating studies from Dr. Satchidananda Panda's lab at the Salk Institute, which link meal timing to metabolic markers independent of what is eaten.

Because the 16:8 window is defined relative to when someone wakes, works, or trains rather than a fixed clock time, people following it need to translate “16 hours fasted” into actual start and stop times for their own day — for example, a last meal at 8 PM means the eating window reopens at noon the next day.

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