Fasting Window Planner
Pick a protocol and a meal time to see exactly when you eat, when you fast, and when fat-burning, ketosis and autophagy kick in.
Beginner-friendly — fast 16h, eat within 8h.
Eating window
12:00 pm – 8:00 pm
8h open
Fasting window
8:00 pm – 12:00 pm (next day)
16h fast
Your fasting stages
Measured from when your fast begins, at 8:00 pm.
Fed · 0–4h · from 8:00 pm
Digesting and absorbing your last meal; insulin is elevated and fat-burning is paused.
Fat-burning · 4–12h · from 12:00 am
Insulin falls, glycogen is being used up and your body shifts towards burning stored fat.
Ketosis · 12–16h · from 8:00 am
Glycogen is largely depleted; the liver makes ketones to fuel your brain and muscles.
Autophagy · 16h+ · from 12:00 pm
Deeper into the fast, cellular 'clean-up' (autophagy) ramps up alongside steady fat-burning.
Fast smarter, not just longer
The free 5-Day Keto Kickstart pairs each day's meals with a fasting schedule, so your window and your macros pull in the same direction.
What happens hour by hour
Fed (0–4h). You're digesting and absorbing your last meal. Insulin is raised to shuttle nutrients into cells, which keeps fat stored rather than burned.
Fat-burning (4–12h). Insulin drops and your body works through its glycogen (stored carbohydrate). As that runs down, it leans increasingly on stored fat for energy.
Ketosis (12–16h). With glycogen largely depleted, the liver starts converting fat into ketones — a clean fuel for your brain and muscles. On a keto diet this arrives sooner.
Autophagy (16h+). Deeper into the fast, cells step up their recycling and repair processes alongside steady fat-burning. This is the stage many longer-fasting protocols are chasing.
These windows are typical averages. Your timing shifts with your diet, activity, sleep and individual metabolism — treat them as a guide, not a guarantee.
Intermittent fasting — your questions answered
How does the fasting window planner work?
Choose a protocol — 16:8, 18:6, 20:4 or OMAD — and tell us when you break your fast. The planner shows your eating window (when you can eat) and your fasting window (when you don't), then maps the metabolic stages relative to the start of your fast: fed, fat-burning, ketosis and autophagy.
What do 16:8, 18:6, 20:4 and OMAD mean?
The numbers are the hours spent fasting versus eating. 16:8 means a 16-hour fast and an 8-hour eating window — the most popular starting point. 18:6 and 20:4 tighten the eating window further. OMAD ('one meal a day') compresses eating into roughly a single hour, for about a 23-hour fast.
When does the body enter ketosis while fasting?
For most people, glycogen stores run low and ketone production picks up around 12–16 hours into a fast — sooner if you're already eating a low-carb or keto diet, because your glycogen starts lower. That's why fasting and keto work so well together: keto primes you to reach ketosis faster.
When does autophagy start?
Autophagy — the cellular 'clean-up' process — is thought to ramp up meaningfully from around 16 hours of fasting and increase the longer you go, though the exact timing varies between individuals and isn't precisely measurable at home. The stages shown here are a useful guide, not a clinical readout.
Can I drink anything during the fasting window?
Yes. Water, black coffee, plain tea and other zero-calorie drinks won't break your fast and help with hunger and hydration. Electrolytes (sodium, potassium, magnesium) are worth adding, especially on keto, to avoid the headaches and fatigue of the 'keto flu'. Anything with calories — milk, sugar, sweeteners that spike insulin — ends the fast.
Is intermittent fasting safe for everyone?
Intermittent fasting suits many people, but it isn't for everyone. If you're pregnant or breastfeeding, under 18, have a history of disordered eating, are underweight, or take medication for diabetes or blood pressure, speak to your doctor first. Start gentle — a 12:12 or 14:10 window — and build up.
Let the timer track your stages live
Keto Club's fasting timer follows your stages in real time and adapts your window to the keto phase you're in.