Calculate your precise eating and fasting windows for any intermittent fasting protocol. Enter your last meal time and fasting duration to see exactly when your next eating window opens.
Enter Your Measurements
Enter hour in 24h format (e.g., 20 = 8 PM)
Results
Fasting Duration
16
hours
Eating Window
8
hours
Eating Window Opens (hour)
12
:00
Eating Window Closes (hour)
20
:00
Formula
How to Use This Calculator
How to Use
- 1
Enter the hour you typically finish your last meal (24h format).
- 2
Select your fasting protocol.
- 3
The calculator shows when you can start eating the next day.
Frequently Asked Questions
Frequently Asked Questions
What is the most popular intermittent fasting protocol?
Can I drink during the fasting window?
In-Depth Guides
Intermittent Fasting: How It Works and How to Start
A practical guide to intermittent fasting protocols, benefits, and how to calculate your eating window.
Intermittent Fasting for Beginners: Methods, Benefits, and How to Start
A complete beginner's guide to intermittent fasting covering 16:8, 5:2, and other protocols, with realistic expectations and how to get started.
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About This Calculator
This calculator uses the formula: Eating Window Start = Last Meal Time + Fasting Hours (mod 24). All calculations follow industry-standard methods. Results are estimates — always verify with a licensed professional for structural or code-compliant work.
Built and maintained by the CalcSmart team. Last updated March 2026.
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