Intermittent Fasting Calculator
Turn 16:8 (or any fast length) into clock times from when you start eating. Click any i for detail.
Schedule
Fast length (hours)
i
Fast
Hours without calories (16 for classic 16:8). |
|
|---|---|
Eat start (HH:MM, 24h)
i
Start
When your eating window begins. |
How to use this calculator
- Enter how many hours you fast.
- Enter when eating starts (24-hour HH:MM).
- Read eat-end / fast-start and the next eat time.
- Adjust with your clinician if you have medical constraints.
Results explained
If you fast F hours, you eat for 24−F hours. Starting the eat window at a clock time, the fast begins when that window ends. Popular patterns include 16:8, 18:6, and 20:4. This page does not prescribe fasting for weight loss or medical conditions.
Quick reference: IF windows
eat_hours = 24 − fast_hours.
| Item | Detail |
|---|---|
| 16:8 | 16 h fast, 8 h eat |
| 18:6 | 18 h fast, 6 h eat |
| OMAD-ish | ~23 h fast / 1 h eat |
| Black coffee | Often allowed in protocols — follow yours |
Educational schedule sketch — not medical or nutrition therapy.
How the estimate is built
eat_end = start + (24 − fast); next_eat = eat_end + fast (mod 24h).
Example scenario
16 h fast, eat start noon → eat until 8:00 PM, fast overnight, eat again at noon.
FAQ
Can I drink water while fasting?
Most protocols allow water; some allow black coffee/tea. Follow the protocol you chose.
What if I wake at 7 AM?
Set eat start to whenever your window opens — the math is clock-based, not wake-based.
Is IF safe for everyone?
No. Pregnancy, history of disordered eating, and some medications need clinician guidance.
Does the window have to be daily?
This page models a daily repeating window only.