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
⏱ Fasting Stages
What Happens Inside Your Body
Live biological stages during your 16-hour fast — each backed by peer-reviewed research.
Last Meal Completed
+0hYour fasting clock starts now. Digestion begins and your body processes the glucose from your last meal.
📄 Mayo ClinicDigestion Phase
+2hBlood glucose peaks and insulin is released. Your body is actively digesting and storing nutrients from the last meal.
📄 NIH — Metabolism OverviewBlood Sugar Stabilizing
+4hInsulin levels begin to drop. Blood sugar returns toward baseline. Your body shifts from storing to maintaining.
📄 PubMed — Insulin & Glucose DynamicsGlycogen Depleting
+8hLiver glycogen stores are running low. Your body begins mobilising free fatty acids as an alternative fuel source.
📄 Cahill GF Jr — NEJM 1970🔥 Ketosis Begins
+12hGlycogen stores are nearly depleted. Your liver starts producing ketone bodies from fat — your brain switches to fat-burning mode.
📄 Cahill GF Jr — NEJM 1970✨ Autophagy Activates
+16hCellular housekeeping begins. Your cells start breaking down damaged proteins and organelles — a key anti-aging mechanism.
📄 Levine & Kroemer — Cell 2008* Biological timelines are approximate and vary by individual. Sources: PubMed, NIH, Cell journal.
⏱ Live Timer
Track Your Fast in Real Time
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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.
Ketosis typically begins at 12–14 hours of fasting, and autophagy (cellular repair) activates around the 16-hour mark — making 16:8 an optimal balance of benefits and practicality.
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