Fasting window calculator
This tool tells you when your eating window opens. Enter the time your last meal ended and pick your fasting protocol; it adds the fasting hours and shows the earliest time you can eat again. On 16:8 you fast for 16 hours, so a last meal at 8:00 PM means you can eat again at 12:00 PM the next day.
Better Fasting is a free intermittent-fasting tracker for web, iPhone, Apple Watch, Android and Chrome, with an optional one-time Pro upgrade and no subscription.
Fasting windows at a glance
Every everyday protocol is a split of a 24-hour day: fast for the first number, eat within the second. Longer fasts of 24 hours and up are not windows. Past a day, the non-fasting time is whatever is left of your week.
| Protocol | Fasting | Eating window |
|---|---|---|
| 12:12 | 12 hours | 12 hours |
| 14:10 | 14 hours | 10 hours |
| 16:8 | 16 hours | 8 hours |
| 18:6 | 18 hours | 6 hours |
| 20:4 | 20 hours | 4 hours |
| OMAD | 23 hours | about 1 hour (one meal) |
How the calculation works
Take the clock time your last meal ended and add your protocol's fasting hours. The number before the colon is the fasting length: 16:8 is a 16-hour fast, 18:6 is 18, 20:4 is 20. OMAD (one meal a day) is treated as a 23-hour fast. If the total passes midnight, your eating window opens the following day.
Does the exact window matter?
Not to the minute. The window is a target, not a rule you can fail by being a little early or late. Consistency day to day matters more than hitting an exact clock time, which is why Better Fasting tracks the streak rather than policing the boundary.
Ready to track it? Start a fast. No account needed to begin.