36-hour fast calculator
Enter when you finish eating and choose the days your fast starts on. The calculator shows when each 36-hour fast ends.
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How a 36-hour fast is timed
A 36-hour fast runs from the end of dinner, through the whole of the next day, to breakfast the day after. Finish at 7:00 PM on Monday and it ends at 7:00 AM on Wednesday.
On this page the fast is tied to weekdays you choose, with ordinary eating on the other days. That is different from alternate-day fasting, where fasts follow one another every two days. Two starting days need at least two days between them, so that one fast ends, with time to eat, before the next begins.
A 36-hour fast is a long fast and is not suitable for everyone. Please read the safety information before planning one.
Questions
If I start a 36-hour fast after dinner on Monday, when does it end?
Thirty-six hours after you finished eating. From 7:00 PM on Monday that is 7:00 AM on Wednesday. Enter your own time above to see yours.
Can I choose more than one day a week?
Yes, as long as the days are far enough apart. Monday and Thursday work. Monday and Tuesday do not, because the first fast would still be running when the second was due to start.
What happens when the clocks change?
A fast is measured in real hours. On the night the clocks go back, a 16-hour fast that starts at 8:00 PM ends at 11:00 AM by the clock, not at noon. The calculator and the tracker both count real hours, and the calculator marks any fast that has a clock change inside it.
Is this medical advice?
No. The calculator does arithmetic on times. It knows nothing about your health and cannot tell you whether fasting, or a fast of this length, is suitable for you. Talk to a healthcare professional before you start, and read the safety information.