16/8 Intermittent Fasting Calculator — Find Your Eating Window
Enter the time of your last meal and select your fasting protocol. The calculator tells you exactly when to break your fast and shows your full daily schedule split between fasting and eating. Works for 16/8, 18/6, and OMAD (20/4).
In 16/8 intermittent fasting you fast for 16 hours and eat within an 8-hour window. If your last meal is at 8:00 PM, you break your fast at 12:00 PM the next day. For 18/6, last meal at 8 PM → break fast at 2 PM. For OMAD (20/4), last meal at 8 PM → break fast at 4 PM.
When to use this calculator
- Find the exact time to break your fast each day on 16/8
- Compare 16/8 vs 18/6 vs OMAD eating windows side by side
- Plan meals around work, gym, and social schedules
- Students and dietitians studying time-restricted eating protocols
- Quick daily reference when starting a new fasting routine
Worked Example
- Last meal: 8:00 PM (20:00), protocol: 16/8
- 16 hours after 20:00 = 12:00 (noon) next day
- Eating window: 12:00 PM – 8:00 PM (8 hours)
How it works
2 min readHow the 16/8 intermittent fasting schedule works
The calculator adds your fasting hours to your last-meal time and wraps around midnight if needed. The formula is:
Break-fast time = last meal time + fasting hours
For example, last meal at 8 PM (20:00) + 16 hours = 12:00 PM (noon).
Common 16/8 eating windows — quick reference table
| Last meal (start fast) | Protocol | Break-fast time | Eating window |
|---|---|---|---|
| 6:00 PM (18:00) | 16/8 | 10:00 AM | 10 AM – 6 PM |
| 7:00 PM (19:00) | 16/8 | 11:00 AM | 11 AM – 7 PM |
| 8:00 PM (20:00) | 16/8 | 12:00 PM | 12 PM – 8 PM |
| 9:00 PM (21:00) | 16/8 | 1:00 PM | 1 PM – 9 PM |
| 10:00 PM (22:00) | 16/8 | 2:00 PM | 2 PM – 10 PM |
| 8:00 PM (20:00) | 18/6 | 2:00 PM | 2 PM – 8 PM |
| 8:00 PM (20:00) | OMAD 20/4 | 4:00 PM | 4 PM – 8 PM |
Protocol comparison
| Protocol | Fast | Eating window | Best for |
|---|---|---|---|
| 16/8 | 16 hours | 8 hours | Beginners, sustainable long-term |
| 18/6 | 18 hours | 6 hours | Intermediate, faster fat loss |
| OMAD (20/4) | 20 hours | 4 hours | Advanced, maximum simplicity |
What can break a fast
Why the eating window placement matters
Research from the Salk Institute suggests early time-restricted eating (eating window ending before 6–8 PM) may align better with circadian metabolism. However, most people get good results regardless of window timing as long as the fasting duration is maintained consistently.
When to consult a healthcare professional
Frequently asked questions
If I eat my last meal at 8 PM, when do I break my fast on 16/8?
At 12:00 PM (noon) the next day. 8 PM + 16 hours = 12 PM. Your eating window is then 12 PM to 8 PM — exactly 8 hours.
If I eat my last meal at 7 PM, when do I break my fast?
At 11:00 AM the next day (7 PM + 16 hours = 11 AM). Your eating window shifts to 11 AM – 7 PM.
What is the difference between 16/8 and 18/6 fasting?
16/8 means 16 hours fasting with an 8-hour eating window; 18/6 means 18 hours fasting with a 6-hour eating window. With the same 8 PM last meal, 16/8 lets you eat from 12 PM, while 18/6 only lets you eat from 2 PM.
Does sleeping count toward fasting hours?
Yes. Sleep is the easiest part of your fast. A typical 7–8 hour sleep covers most of your 16-hour window, leaving only 8–9 waking hours where you are not eating.
Can I drink coffee during the fasting window?
Plain black coffee (no milk, cream, or sugar) is generally considered fast-safe. It contains negligible calories and does not spike insulin in most people. Bulletproof coffee with fat does break the fast.
How long does it take to adapt to 16/8 fasting?
Most people adapt within 1–2 weeks. The first 3–5 days may include hunger pangs, especially in the morning. After adaptation, many people report reduced hunger during the fasting window.
Is 16/8 intermittent fasting safe for women?
Research shows mixed results. Some women do well on 16/8; others report hormonal disruption (irregular cycles, sleep issues) and do better with a gentler 14/10 approach. Start conservatively and adjust based on your body's response.
Can I work out while fasting on 16/8?
Light to moderate cardio during the fasting window is generally fine and may enhance fat oxidation. Heavy resistance training is best scheduled close to or within your eating window so you can refuel with protein immediately after.
Does 16/8 fasting actually work for weight loss?
Systematic reviews (e.g., Cioffi et al. 2018, Harris et al. 2018) find that 16/8 produces modest weight loss similar to continuous caloric restriction when total calorie intake is controlled. The main advantage is simplicity — fewer meals to plan.
Sources and references
- Cioffi et al. (2018) — Intermittent vs. Continuous Energy Restriction on Weight Loss — Nutrients
- Sutton et al. (2018) — Early Time-Restricted Feeding Improves Insulin Sensitivity — Cell Metabolism
- Lowe et al. (2020) — Time-Restricted Eating for Weight Loss — NEJM Evidence
- Salk Institute — Circadian Time-Restricted Eating Research