IFWindow

Intermittent Fasting Calculator

16:8, 18:6, OMAD — pick any protocol.

Fasting hours

Break-fast time

Eating window: 8 hours
Break fast at: 12:00 PM
Stop eating at: 8:00 PM
Fasting protocol: 16:8

What you entered

Fasting hours: 16Break-fast time: 12:00

1
Eating window length
24 − 16= 8 hours
2
Break fast at
12:00= 12:00 PM
3
Stop eating at (start of next fast)
12:00 PM + 8h= 8:00 PM

Result

Eating window: 8 hours

On a 16:8 protocol starting at 12:00 PM, eat between 12:00 PM and 8:00 PM, then fast until the next day.

Eating windows for common fasting protocols

Each protocol splits the day into a fasting period and an eating window. These rows show when the window opens and closes for a chosen first meal.

Protocol	Fast	Eating window	First meal	Last meal by
12:12	12 h	12 h	8:00 AM	8:00 PM
14:10	14 h	10 h	10:00 AM	8:00 PM
16:8	16 h	8 h	12:00 PM	8:00 PM
18:6	18 h	6 h	1:00 PM	7:00 PM
20:4	20 h	4 h	5:00 PM	9:00 PM

Fasting is not suitable during pregnancy, with a history of eating disorders, or alongside diabetes medication without medical supervision. General wellness information only, not medical advice. Discuss any health decision with a qualified clinician.

The numbers behind the protocol names

16:8 means 16 hours fasting, 8 hours eating each day; 18:6 is stricter; OMAD ('one meal a day') is the extreme end — this calculator just does the clock math to show your exact eating window for any split.

Why the specific window matters

Knowing exactly when your eating window opens and closes removes the guesswork and decision fatigue of tracking fasting hours manually throughout the day.

Frequently asked questions

What is the best intermittent fasting schedule?

16:8 is the most popular and sustainable: fast 16 hours, eat during an 8-hour window (e.g., noon to 8 PM). 18:6 and 20:4 are stricter. OMAD (one meal a day) is the most extreme. Start with 16:8 — it's easy to follow (skip breakfast, eat lunch and dinner) and has the most research support.

Does intermittent fasting help you lose weight?

Yes, primarily by reducing total calorie intake — eating in a shorter window naturally leads to fewer meals. Studies show IF produces similar weight loss to traditional calorie restriction. It doesn't have a magical fat-burning effect beyond the calorie deficit, but many people find it easier to maintain than counting calories.

What can I consume during the fasting window?

Water, black coffee, and plain tea are fine — they have zero or negligible calories and don't break the fast. Avoid anything with calories, sugar, or artificial sweeteners (which may trigger an insulin response). Bone broth is debated — it technically has calories but many IF practitioners allow it.