Intermittent Fasting Schedule Planner
Enter your last meal time and a fasting protocol (16:8, 18:6, 20:4, or OMAD) to see your exact fasting and eating window times.
Fasting window
8:00 PM – 12:00 PM
Eating window
12:00 PM – 8:00 PM
General fasting-duration stages (approximate, commonly cited)
- 0–4h: Digesting your last meal; blood sugar rises then falls back down.
- 4–16h: Blood sugar and insulin drop toward baseline; the body increasingly draws on stored glycogen.
- 16–24h: Glycogen stores are increasingly depleted; fat-burning and ketone production typically increase.
- 24h+: Some research associates extended fasting with increased autophagy (cellular cleanup) — evidence is still developing and effects vary widely by individual.
These are commonly cited general ranges from fasting research and physiology, not a precise timeline for any individual — actual timing varies significantly by metabolism, recent food intake, activity level, and other factors. This tool schedules your eating/fasting windows only; it is not medical advice and does not track adherence, hunger, or health outcomes.
About this tool
How to use it
- Pick a fasting protocol — 16:8, 18:6, 20:4, OMAD, or a custom number of fasting hours.
- Enter the time your last meal of the day ends.
- Press Calculate Schedule, or just keep typing — your fasting and eating windows update live.
- Read the general fasting-stage list for a rough sense of what's commonly reported at different points in a fast.
Why it matters
Intermittent fasting protocols are usually described as a ratio (like 16:8), but turning that into actual clock times — when your fast starts, when you can eat again, when the next fast begins — takes a bit of arithmetic that's easy to get slightly wrong, especially when the eating window crosses midnight into the next calendar day.
When to use it
Useful when starting a new fasting protocol and wanting exact times to plan meals around, when adjusting your last-meal time and wanting to see how it shifts your whole schedule, or when comparing how different protocols (16:8 vs. 20:4) change your eating window length.
Good to know
This tool schedules fasting and eating windows only — it does not track whether you actually stuck to the schedule, log meals, or monitor any health outcome. The fasting-stage list gives commonly cited general ranges from fasting physiology research, not a precise timeline for any individual; actual timing of things like glycogen depletion or ketone production varies significantly by metabolism, recent food intake, activity level, and other individual factors.
Common questions
What do the numbers in a protocol like 16:8 mean?
The first number is hours of fasting, the second is hours of eating — 16:8 means a 16-hour fast followed by an 8-hour eating window, repeating daily. All four together (fasting + eating) always add up to 24 hours.
Is intermittent fasting safe for everyone?
This tool doesn't make that judgment — intermittent fasting isn't appropriate for everyone (including some people with diabetes, a history of disordered eating, who are pregnant or breastfeeding, or with certain other health conditions). Talk to a doctor before starting any fasting protocol, especially if you have an existing health condition.
Why does the eating window sometimes show a time after midnight?
If your fasting hours plus your last-meal time push the eating window past midnight, the calculator correctly wraps to the next day rather than showing an invalid time — the actual elapsed hours are always exactly what you selected, regardless of which calendar day the clock time falls on.
What is OMAD?
OMAD stands for 'One Meal A Day' — a 23:1 protocol with a single one-hour eating window and 23 hours of fasting, one of the more restrictive common intermittent fasting patterns.
What actually happens during a fast?
Very broadly and approximately: your body first digests your last meal and uses recently eaten food for energy, then shifts to using stored glycogen as blood sugar drops, and eventually (as glycogen depletes over roughly 16-24+ hours) increases fat-burning and ketone production. Some research links longer fasts to increased autophagy (cellular cleanup), though this is an active area of study with real individual variation — see the fasting-stage list on this page for the general ranges, disclosed as approximate.