Intermittent Fasting Calculator

How to use

1. 1Pick a fasting protocol: 12:12, 14:10, 16:8, 18:6, 20:4, OMAD, 5:2, Eat-Stop-Eat, or Custom for any fasting and eating hours you want.
2. 2Set the date and time your fast started. Use Start now to anchor to the current moment, or Tomorrow 8 AM to plan ahead.
3. 3Read the end of fast time and the end of the eating window (when one applies) in your chosen 12 or 24 hour format.
4. 4Watch the live status card for the current phase, time remaining, and the progress bar that updates every 30 seconds.
5. 5Use the 7 day preview to see how the schedule lands across the upcoming week, or Copy summary to paste the full plan into your tracker or calendar.

About this tool

Intermittent Fasting Calculator answers the question every IF schedule actually needs: given the protocol you follow and the time your fast began, when do you break it, and when does the eating window close? Pick from the schedules people actually run: 12:12 (a gentle starting point), 14:10, 16:8 (the Leangains pattern, by far the most common), 18:6 (a small step up for aggressive deficits), 20:4 (the Warrior diet, one larger evening meal plus light snacks), 23:1 OMAD (One Meal A Day), the 5:2 diet (eat normally five days, very low calorie on two non-consecutive days), and Eat-Stop-Eat (a 24 hour fast once or twice a week). A Custom mode lets you set any fasting and eating hours from one hour up to a 72 hour fast for personalized splits. Choose a start date and time (the Start now button uses the current moment; Tomorrow 8 AM jumps to a planned morning start), and the tool reports the exact wall-clock end of fast, the exact end of the eating window when one applies, the relative day shift (same day, next day, or +N days), and the total duration of each window in hours and minutes. The live status card shows your current phase, fasting or eating, with a countdown of time remaining, time elapsed, and a percentage progress bar that ticks every 30 seconds. A 7 day rolling preview lays out the schedule across the upcoming week so you can see where the eating window lands on a workday versus a weekend, and a copyable plain-text summary captures the full plan for Notes, a habit tracker, a Google Calendar event, or a meal-planning template. Output supports both 12 hour (AM/PM) and 24 hour wall-clock formats. Everything runs locally; protocol, start time, and schedule never leave your browser. This is a planning tool for healthy adults; it is not medical advice. Talk to a clinician before starting a fasting protocol if you are pregnant, breastfeeding, taking medication, or managing a medical condition.

Free to use. Works in your browser. No signup, no login.