Our free intermittent fasting calculator helps you plan your fasting schedule with popular IF protocols — 16:8, 18:6, 20:4, and OMAD. Simply enter your last meal time and choose a fasting protocol to instantly calculate when your fast starts and ends, your eating window, and how much longer you need to fast.
16:8 Fasting Schedule (Last meal: 8:00 PM):
Stay hydrated with water, black coffee, or plain tea during your fast. Break your fast with protein-rich foods.
Select your fasting method: 16:8, 18:6, 20:4, or OMAD.
Enter when you finished your last meal — your fast starts here.
See exactly when to break your fast and your eating window.
Check how many hours remain in your current fast.
In intermittent fasting, you cycle between fasting and eating windows. For 16:8, you fast 16 hours and eat within an 8-hour window. For 18:6, you fast 18 hours with a 6-hour eating window. The calculator computes your eating window based on your last meal time.
Eating Window End = Fast Start + Protocol Fast Hours
Start with 12:12 or 16:8 before attempting 20:4 or OMAD
Stay hydrated during your fasting window — water, black coffee, and plain tea are allowed
Autophagy (cellular cleanup) typically starts at 16–18 hours of fasting
Break your fast with a balanced, protein-rich meal
Consistency matters more than perfection — same eating window daily is ideal
Avoid high-sugar foods when breaking your fast to prevent blood sugar spikes
Our free intermittent fasting calculator helps you plan your fasting schedule for 16:8, 18:6, 20:4, and OMAD protocols. Enter your last meal time to see exactly when to break your fast, your eating window, and your current fasting progress.
The 16:8 method is the most popular intermittent fasting schedule. Fast for 16 hours and eat within an 8-hour window. A typical schedule is eating between 12 PM and 8 PM. Enter your preferred last meal time to generate your personalized 16:8 fasting schedule.
More advanced protocols offer greater benefits for fat loss and autophagy. The 18:6 fast gives a 6-hour eating window, 20:4 gives 4 hours, and OMAD (23:1) means one meal per day. Our calculator supports all protocols and adjusts your eating window and break-fast time accordingly.
Understanding what happens during your fast helps you stay motivated. After 12 hours, glucose stores deplete and fat burning begins. After 16–18 hours, autophagy (cellular cleanup) activates. After 24 hours, growth hormone levels spike. After 48–72 hours, immune system reset begins.
Start with 16:8 — it's the most evidence-backed and beginner-friendly protocol. Pick an eating window that fits your lifestyle (e.g. 12 PM – 8 PM). After 2–4 weeks, consider advancing to 18:6 for greater benefits. Consistency is more important than which protocol you choose.
Data sourced from trusted institutions
All formulas verified against official standards.