Intermittent Fasting · 18-Hour Fast
18:6 Fasting Calculator
18:6 provides a six-hour eating window. Enter your eating start time to calculate the schedule; a longer fast does not guarantee greater health benefits.
Step 1 — Choose Your Protocol
Intermediate — fast 18h, eat within a 6h window.
Step 2 — Personalise Your Schedule
Your eating window starts from this time
🎯 Your Goal
⏱ Time Checkpoints
Your Fasting Timeline
Elapsed-time checkpoints for a 18-hour schedule. These do not measure metabolic changes.
Fast Started
+0hThe clock measures time since your last calories. It does not measure digestion or metabolic changes.
📄 Mayo ClinicEarly Fasting
+2hDigestion and nutrient absorption vary with the meal and the individual.
📄 NIH — Metabolism OverviewBetween Meals
+4hYour body uses a mixture of fuels. Time alone cannot identify your blood glucose or insulin level.
📄 PubMed — Insulin & Glucose DynamicsOvernight Interval
+8hAn overnight interval may include sleep. Glycogen use varies with diet and activity.
📄 Cahill GF Jr — NEJM 197012 Hours Elapsed
+12hTwelve hours is a time checkpoint, not a diagnosis of ketosis. Ketone production varies between people.
📄 Cahill GF Jr — NEJM 197016 Hours Elapsed
+16hSixteen hours does not establish autophagy activation. There is no validated universal human autophagy timer.
📄 Levine & Kroemer — Cell 2008Time checkpoints are educational, not a recommendation to extend your fast.
Why Choose 18:6?
The 18:6 protocol extends the fasting interval by two hours compared with 16:8. It leaves six hours for meals, which may make adequate nutrition harder to fit in. It does not establish a particular metabolic state.
18:6 is ideal for those who have adapted to 16:8 and want to increase the metabolic and cellular repair benefits of fasting without going to the extreme of OMAD.
Medical Disclaimer
This tool provides estimates for informational purposes only. Always consult a licensed healthcare provider before beginning any fasting protocol — especially if you are pregnant, have a history of eating disorders, diabetes, or any other medical condition.
Sources: Mayo Clinic · NIH · PubMed