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Dental Implant Cost Invisalign vs Braces Teeth Whitening Cost Caffeine Half-Life Sleep Debt Period Calculator All 14 tools →Explore 14 free toolsBy Chris Leo · ✓ Based on published intermittent fasting research · Updated July 2026
Quick answer: A 16:8 fasting schedule means eating within an 8 hour window and fasting for 16, water and black coffee allowed. If your first meal is at noon, you finish eating by 8 pm. Use the calculator below to map any fasting plan onto your day.
During the fast: water, black coffee, and plain tea are fine. Anything with calories breaks it.
🔒 Calculations happen in your browser. Nothing you enter is stored or sent anywhere.
Every intermittent fasting plan is a clock split: hours you fast and hours you eat. The calculator anchors your chosen plan to the time you actually want your first meal, then maps the full day: when your eating window closes, when the fast starts, and when it ends tomorrow. No calorie math, no food rules, just a schedule your routine can survive.
Research on intermittent fasting shows meaningful benefits for some people, mostly through easier calorie control and steadier eating patterns. Reviews in major journals find weight-loss results roughly comparable to ordinary calorie restriction, so pick the pattern you can keep, not the most extreme one.
| Plan | Fast / eat hours | Best for |
|---|---|---|
| 12:12 | 12 / 12 | Beginners, first two weeks |
| 14:10 | 14 / 10 | Gentle daily rhythm |
| 16:8 | 16 / 8 | The most studied and most sustainable |
| 18:6 | 18 / 6 | Experienced fasters |
| 20:4 | 20 / 4 | Short-term, experienced only |
| OMAD 23:1 | 23 / 1 | One meal a day, hardest to sustain |
Longer fasts are not automatically better. Consistency over months beats intensity over days.
The best window is the one that overlaps your social reality. If family dinner is at 7 pm, a noon-to-8 window works; a 10-to-6 window collapses the first weekend. Shift workers should anchor the window to their personal “morning,” whatever the clock says.
Eight hours of the fast can happen while you sleep. Finishing dinner by 8 pm and sleeping 11 pm to 7 am puts you 11 hours into a 16 hour fast before breakfast time. That is why most people find 16:8 far easier than it sounds.
Water, black coffee, and plain tea are fine and help with hunger. Diet soda sits in a gray zone; most researchers count it as not breaking a fast, though it can trigger cravings. Milk, sugar, juice, and anything with meaningful calories ends the fast.
Jumping straight to 20:4 is the fastest way to quit by Friday. Start at 12:12 for a week or two, move to 14:10, then 16:8. Hunger waves pass in 15 to 20 minutes; a glass of water and a walk beat white-knuckling it.
Pick 16:8 or gentler, set your window with the calculator, and hold it for two weeks before judging. Keep protein high in your first meal so the window does not turn into a carb crash. Expect the first three to five days to feel odd while your routine adjusts. And skip fasting entirely on days you are sick, doing intense training you have not fueled, or short on sleep; forcing it makes everything worse.
Intermittent fasting is an eating pattern that cycles between set fasting and eating periods, like 16 hours fasting with an 8 hour eating window. It does not prescribe foods, only timing. Popular versions include 16:8, 18:6, and one meal a day (OMAD).
During a fast, insulin levels fall and your body leans more on stored energy. In practice, most of the measurable benefit comes from eating fewer calories with less effort: a shorter eating window usually means fewer snacks and late-night calories, which supports steady weight management.
Start with a 12:12 split for one to two weeks, then extend the fast by an hour or two per week until you reach 16:8. Anchor your eating window to your real schedule, keep water and black coffee handy during the fast, and hold the plan for two weeks before deciding.
Yes, black coffee is fine during a fast; it has roughly 2 calories and does not meaningfully raise insulin. Add milk, cream, sugar, or syrup and the fast is broken. Late-day coffee can hurt your sleep, so keep it to the first half of your fast.
Yes, and you should. Water, sparkling water, and plain tea keep you hydrated and blunt hunger waves during the fast. Dehydration is behind many “fasting headaches”, so drink through the fasting hours, not just in the eating window.
For your safety
Who should not fast: This planner is for healthy adults. Do not use intermittent fasting if you are pregnant or breastfeeding, under 18, have diabetes treated with insulin or sulfonylureas, or have any history of an eating disorder. If you take daily medication with food, ask your doctor before changing meal timing. This tool is a schedule planner, not medical or nutrition advice.
Disclaimer: These statements have not been evaluated by the Food and Drug Administration. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.
