Intermittent Fasting · 16-Hour Fast
16:8 Fasting Calculator
Enter your preferred eating start time to get your exact 16:8 fasting schedule, calorie targets, and biological milestone timeline.
Step 1 — Choose Your Protocol
16:8 is the most popular protocol — fast 16h, eat within 8h.
Step 2 — Personalise Your Schedule
Your eating window starts from this time
🎯 Your Goal
⏱ Time Checkpoints
Your Fasting Timeline
Elapsed-time checkpoints for a 16-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.
Live fasting timer
Planned fast
16:00:00
16h fasting · 8h eating
Fasting window —
Eating estimate —
Your timer and last seven finished sessions stay in this browser.
What Is the 16:8 Fasting Method?
The 16:8 intermittent fasting protocol is the most studied and practised form of time-restricted eating. You fast for 16 consecutive hours and consume all your meals within an 8-hour window.
A 2020 study published in JAMA Internal Medicine (Lowe et al.) found that 16:8 fasting significantly reduced calorie intake and supported healthy weight management without requiring calorie counting.
A 16-hour schedule does not guarantee ketosis or increased autophagy. These processes cannot be measured by a schedule calculator, and the suitability of fasting depends on your health and nutritional needs.
16:8 Fasting — FAQs
What is the 16:8 fasting method?
The 16:8 method involves fasting for 16 consecutive hours and eating all your meals within an 8-hour window each day. It's the most popular intermittent fasting protocol due to its flexibility — most people fast overnight and skip breakfast.
What can I drink during the 16-hour fast?
Water, black coffee, plain tea, and sparkling water are generally considered safe during a 16:8 fast. Avoid anything with calories, including milk, sugar, or juice, as these can break your fast.
When is the best eating window for 16:8?
Most people find 12:00 PM – 8:00 PM works well, aligning with social meals. However, research suggests earlier eating windows (e.g. 8 AM – 4 PM) may offer additional metabolic benefits.
Can I do 16:8 every day?
Yes. The 16:8 method is designed to be a sustainable daily practice. Studies show it's safe long-term for most healthy adults (Lowe et al., JAMA 2020).
How long until I see results with 16:8?
Most people notice reduced appetite within the first week. Weight changes typically become visible after 3–4 weeks of consistent practice combined with appropriate calorie intake.
Try Other Protocols
Not sure 16:8 is right for you? Compare alternatives.
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