Intermittent fasting calculator
Pick a method and say when you last ate. The calculator lays out the fasting and eating windows for that method.
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The methods compared by the clock
The daily methods split each 24 hours into a fast and an eating window: 16:8 is 16 hours fasting and 8 hours eating, 18:6 is 18 and 6, 20:4 is 20 and 4, and OMAD (one meal a day) is about 23 and 1.
Alternate-day fasting, as timed here, is a 36-hour fast followed by a 12-hour eating window, repeating every two days. A 36-hour fast can also be done on chosen weekdays, with ordinary eating in between.
The methods differ in how long the fast is and how often it comes round. This page shows the times for each; it does not rank them or recommend one.
Questions
Which method should I choose?
That depends on your health, your routine and what a healthcare professional advises, none of which a calculator can weigh. This page only shows what each method's schedule looks like so you can compare the times.
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.
What does Start this fast do?
It opens the ADF Chronicles tracker with this schedule filled in and shows you what it will do. Nothing is saved until you confirm there. The tracker then counts down the fast, keeps a calendar and records how each fast went, on your own device with no account.
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.