Intermittent Fasting Calculator
Plan your eating and fasting windows
Use this when you need a fast, accurate result — no sign-up, works entirely in your browser.
Eating window start—
Eating window end—
Fasting hours—
Fasting ends at—
How to Use
- Enter your details into the fields above.
- Click the calculate button to get your result instantly.
- Use the clear button to start a new calculation.
Example
- 16:8 protocol, first meal at 12:00 → Eating window 12:00–20:00; fast 16 hours; fasting ends 12:00 next day
- 18:6 protocol, first meal at 12:00 → Eat 12:00–18:00, fast 18 hours
Formula
Eating window length = 24 − fasting hours, counted from the first meal. The fasting window is everything outside it. Most people find it easiest to place the eating window around their normal waking hours and to drink water, black coffee, or plain tea during the fast.
About Intermittent Fasting Calculator
Plan your eating and fasting windows. This free online tool gives you fast, accurate results without registration or downloads.
Everything runs locally in your browser, so your data is never uploaded or stored — privacy first.
Frequently Asked Questions
Is this tool free to use? +
Yes, it is completely free with no registration or download required.
Is my data private? +
Yes. Everything is processed locally in your browser. Nothing is uploaded or stored on our servers.
Does it work on mobile? +
Yes, it works on any device — phone, tablet, or desktop.