Question 1

How does this intermittent fasting calculator work?

Accepted Answer

Pick a fasting protocol (16:8, 18:6, 20:4, OMAD, 14:10, or a custom split) and tell it when your current fast started — usually the time of your last meal. The timer then repeats that fasting-and-eating split every 24 hours and shows you whether you are currently fasting or eating, how much time has elapsed in the current phase, and how much time is left until it ends.

Question 2

What do 16:8, 18:6, and 20:4 mean?

Accepted Answer

The first number is how many hours you fast; the second is how many hours you have to eat, and the two always add up to 24. 16:8 means 16 hours fasting and an 8-hour eating window — the most common starting protocol. 18:6 and 20:4 are stricter versions with shorter eating windows. OMAD ("One Meal A Day") is the extreme case: 23 hours fasting with just a 1-hour eating window.

Question 3

What is a custom fasting schedule?

Accepted Answer

If none of the standard protocols fit your routine, choose "Custom" and enter any fasting length between 1 and 23 hours. The calculator automatically sets your eating window to whatever is left in the 24-hour day (for example, a 13-hour fast leaves an 11-hour eating window).

Question 4

Can I drink water, coffee, or tea during my fasting window?

Accepted Answer

Most intermittent fasting approaches allow zero-calorie drinks — plain water, black coffee, and unsweetened tea — during the fasting window, since they do not meaningfully break a fast. Adding sugar, milk, or cream introduces calories that many practitioners count as ending the fast. This tool only tracks time, not what you consume, so check the guidance for your specific goals.

Question 5

What about the 5:2 diet — why isn't it a protocol option here?

Accepted Answer

The 5:2 diet is a different style of intermittent fasting: instead of a daily fasting-and-eating window, you eat normally five days a week and restrict calories (roughly 500–600) on two non-consecutive days. Because it is measured in calories per day rather than a repeating daily window, it doesn't fit this timer's hours-based model — the protocols above (16:8, 18:6, 20:4, OMAD, 14:10, custom) are all daily time-restricted eating schedules.

Question 6

Is intermittent fasting safe for everyone?

Accepted Answer

This tool is for informational and scheduling purposes only, not medical advice. Intermittent fasting is not recommended for pregnant or breastfeeding people, those with a history of eating disorders, people with diabetes on glucose-lowering medication, children, or anyone with an underlying health condition without first talking to a doctor.

Question 7

Why did my timer reset or show the wrong phase?

Accepted Answer

The calculator repeats your chosen protocol every 24 hours starting from the fast-start time you entered. If the phase looks wrong, double-check that the "fast start time" field reflects when you actually stopped eating for this fast — updating it (or pressing "Start Fast Now") recalculates everything from that new starting point.

Protocol	Fasting	Eating Window
14:10	14h	10h
16:8	16h	8h
18:6	18h	6h
20:4	20h	4h
OMAD (23:1)	23h	1h
Custom	1–23h	24h − fasting hours

Intermittent Fasting Window & Timer Calculator

Your Fast

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Fasting Protocol Reference

How This Calculator Works

Frequently Asked Questions

How does this intermittent fasting calculator work?

What do 16:8, 18:6, and 20:4 mean?

What is a custom fasting schedule?

Can I drink water, coffee, or tea during my fasting window?

What about the 5:2 diet — why isn't it a protocol option here?

Is intermittent fasting safe for everyone?

Why did my timer reset or show the wrong phase?

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