Intermittent Fasting Schedule Calculator
Pick a fasting plan (16:8, 18:6, 20:4, 14:10, 12:12, 23:1 or custom) and your last or first meal time to see when the fast ends and the eating window closes. How it works
Use the Intermittent Fasting Schedule Calculator
About the Intermittent Fasting Schedule Calculator
In a 16:8 plan with the fast beginning at 8:00 PM, the fast ends at 12:00 PM the next day and the eating window closes at 8:00 PM. Plan around your last meal and its time is the start of the fast; plan around your first meal and the page counts back, so a 15-hour fast with the first meal at 12:00 PM begins at 9:00 PM.
The six plans, for a fast that begins at 8:00 PM
| Plan | Fast | Eating window | Midpoint of the fast | Fast ends, eating window opens |
|---|---|---|---|---|
| 16:8 | 16 hours | 8 hours | 4:00 AM | 12:00 PM |
| 18:6 | 18 hours | 6 hours | 5:00 AM | 2:00 PM |
| 20:4 | 20 hours | 4 hours | 6:00 AM | 4:00 PM |
| 14:10 | 14 hours | 10 hours | 3:00 AM | 10:00 AM |
| 12:12 | 12 hours | 12 hours | 2:00 AM | 8:00 AM |
| 23:1 (OMAD) | 23 hours | 1 hour | 7:30 AM | 7:00 PM |
The midpoint and the end fall on the next day. The eating window closes at 8:00 PM, when the next fast begins.
Methodology
Fast ends = start + fasting hours. Midpoint = start + fasting hours ÷ 2. Eating window closes = fast ends + eating hours, which is the hour the next fast begins. The two numbers in a plan name add up to 24, and a Custom plan’s eating window is 24 minus the fasting hours.
How to use this tool
- Choose a plan: 16:8, 18:6, 20:4, 14:10, 12:12 or 23:1, or choose Custom and type the fasting hours, a whole number from 1 to 23.
- Choose Plan around: Last meal (the fast begins then) or First meal (the fast ends then), and type the time to the minute. The default is a last meal at 8:00 PM.
- Read the timeline: fast begins, midpoint, fast ends with the eating window opening, and the eating window closing.
Frequently asked questions
- What time does the eating window open on 16:8?
- Sixteen hours after the fast begins. A fast that begins at 8:00 PM ends at 12:00 PM the next day, one that begins at 7:00 PM ends at 11:00 AM, and one that begins at 9:00 PM ends at 1:00 PM.
- What does 16:8 mean?
- The first number is hours of fasting and the second is hours of eating in the same 24-hour day. The other plans follow the same pattern: 18:6, 20:4, 14:10 and 12:12. The 23:1 plan, called OMAD for one meal a day, is a 1-hour eating window. Custom takes any whole number of fasting hours from 1 to 23 and gives the eating window the rest of the day: a 15-hour fast that begins at 8:00 PM ends at 11:00 AM, a 15:9 day.
- How do I plan an 18:6 schedule?
- Pick the hour your last food ends and start the fast there. With a start at 6:00 PM the fast ends at 12:00 PM the next day, the eating window runs from 12:00 PM to 6:00 PM and the midpoint is 3:00 AM, so lunch and an early dinner fit and breakfast does not.
- What does “Next fast starts” mean?
- It is the next time the fast’s start time comes round on your device’s clock: today if that time is still ahead, otherwise tomorrow. The page reads the clock after it loads and refreshes it every minute, and the timeline uses the same value.
- Does the tool track my fasts or say which plan is best?
- No. It stores nothing, does not log fasts and does not say which plan suits you. The plan notes describe the hours and make no claim about health effects. Ask a healthcare provider before fasting if you are pregnant, have diabetes or take medicine that must be taken with food.
- When does the fast start, and does sleep count?
- It starts when you finish eating, not when you sit down to the meal, so set the hour of your last bite. Sleep counts toward it: on 16:8 with the fast starting at 9 PM, it ends at 1 PM the next day, and the whole night is inside the 16 hours.
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