16:8 vs. 18:6 vs. OMAD: What Actually Differs
How the most common intermittent fasting protocols differ in eating window length, and what that practically means day to day.
The protocols mainly differ in how much of the day you eat within — everything else about the underlying idea is the same.
Side by side
| Protocol | Eating window | What it looks like day to day |
|---|---|---|
| 16:8 | 8 hours | Skip breakfast, eat lunch through early dinner |
| 18:6 | 6 hours | A tighter midday-to-evening window |
| 20:4 | 4 hours | Often one larger meal plus a smaller one |
| OMAD | 1 hour | All food in a single sitting |
What actually changes as the window shrinks
A shorter eating window generally means fitting the same amount of food into fewer meals, which some people find simpler and others find harder to sustain socially — a 1-hour OMAD window leaves little room for a normal lunch or dinner with other people on a different schedule.
Pick a protocol and enter your first meal time into the Intermittent Fasting Calculator to see your exact windows before committing to it.