Intermittent Fasting Calculator
Calculate Intermittent Fasting metrics for training, nutrition, and performance planning.
This intermittent fasting calculator schedules your daily fasting and eating windows based on a chosen fasting protocol (like 16:8 or 18:6) and your preferred start time, showing exactly when your eating window opens and closes each day.
Choose your fasting protocol and preferred start time, and the calculator returns your daily fasting and eating window schedule.
Worked Calculation Examples
| Scenario | Result | Calculation Step |
|---|---|---|
| 16:8 protocol, first meal at 12:00 PM | Eating window 12:00 PM - 8:00 PM | Eating window end = 12:00 PM + 8 hours = 8:00 PM. Fasting resumes at 8:00 PM until 12:00 PM the next day (16 hours). |
| 18:6 protocol, first meal at 1:00 PM | Eating window 1:00 PM - 7:00 PM | Eating window end = 1:00 PM + 6 hours = 7:00 PM. Fasting resumes at 7:00 PM until 1:00 PM the next day (18 hours). |
Common Intermittent Fasting Protocols
16:8 (16 hours fasting, 8-hour eating window) is one of the most popular approaches, though variations like 18:6, 20:4, or alternate-day fasting all follow the same basic principle of restricting eating to a specific time period rather than changing what you eat.
Calculating Your Personal Eating Window
Once you pick a protocol and a start time for your first meal, the calculator simply adds the eating window duration to find your last meal cutoff, and subtracts the fasting window duration from your next day's start to confirm the schedule repeats consistently.
How to Use the Intermittent Fasting Calculator
- Open the Intermittent Fasting Calculator and enter the values requested in the input fields.
- Check the units, percentages, dates, or time periods before reading the answer.
- Review the instant result and adjust any value to compare another scenario.
- Use the formula, example, and FAQs below to understand how the intermittent fasting calculator works.
Frequently Asked Questions
What is 16:8 intermittent fasting?
It's a fasting protocol with a 16-hour fasting window and an 8-hour eating window each day, one of the most common intermittent fasting approaches.
How do I calculate my eating window?
Choose a start time for your first meal, then add your protocol's eating window length (for example, 8 hours for 16:8) to find your cutoff time for the last meal of the day.
Is intermittent fasting safe for everyone?
No - it's not recommended for certain groups, including pregnant or breastfeeding individuals, people with a history of disordered eating, or those with certain medical conditions. Consult a doctor before starting any fasting protocol.
How do I use this intermittent fasting calculator?
Enter the known values, review the units or settings, and the calculator updates the result instantly. The formula and example on this page show how the answer is produced.
What does the Intermittent Fasting Calculator calculate?
Calculate Intermittent Fasting metrics for training, nutrition, and performance planning. It is designed for fast browser-based calculations without sign-up, downloads, or manual spreadsheet setup.
What formula does this intermittent fasting use?
The formula is: Eating Window End = Start Time + Protocol Window (e.g., 8 hours for 16:8). While periodic fasting has roots in centuries-old religious and cultural practices across many traditions, the modern popularization of structured protocols like 16:8 largely dates to the early 2010s, gaining significant research attention after studies on time-restricted eating in both animal models and humans suggested potential metabolic benefits linked to circadian rhythm alignment, an active area of ongoing nutrition science research.
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Last updated: September 27, 2026.