Intermittent fasting window calculator
It helps you set daily intermittent fasting times, with an option for custom fasting hours.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter last meal time, fasting plan and fasting hours (custom plan).
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Break-fast time = last meal time + fasting hours. Eating window = 24 - fasting hours. Window closes = break-fast time + eating window.
Example
Inputs: Last meal time = 20:00, Fasting plan = 16:8, Fasting hours (custom plan) = 16 hours. Result: Break the fast at: 12:00 (next day); Eating window closes: 20:00 (next day); Fasting hours: 16 hours.
Limits and caveats
- Intermittent fasting is not suitable for pregnant or breastfeeding women, people with diabetes on insulin or a history of eating disorders without medical advice.
- The tool only works out times; it does not plan what to eat.
Questions about this tool
What does 16:8 mean?
You fast for 16 hours in a row and eat within 8 hours, for example from 12 noon to 8 pm.
Does water or black coffee break the fast?
Plain water, black coffee and unsweetened tea are usually allowed because they have almost no calories.
Which plan should I start with?
Many people begin with 12:12 or 14:10 and move to 16:8 gradually.