Health calculator
Intermittent Fasting Calculator
Fasting end time, eating window, and milestones for 16:8, 18:6 or OMAD.
Quick answer
If I stop eating at 8 PM, when does a 16:8 fast end?
A 16:8 fast that starts at 8:00 PM ends at 12:00 PM (noon) the next day. Your 8-hour eating window runs from 12:00 PM to 8:00 PM, then the next fast begins.
Fast end = last meal time + fasting hours. Eating window = 24 − fasting hours.
⚡ Answer updates as you type · Enter = calculate · Esc = reset
- Fast ends = 8:00 PM + 16 hours = 12:00 PM (next day).
- Eating window = 24 − 16 = 8 hours, from 12:00 PM (next day) to 8:00 PM (next day).
- 4 hours, at 12:00 AM (next day): Blood sugar settles after your last meal.
- 8 hours, at 4:00 AM (next day): Stored glycogen starts running low.
- 12 hours, at 8:00 AM (next day): Body shifts toward fat burning.
- 16 hours, at 12:00 PM (next day): Early ketosis for many people.
- Estimates only — everyone is different. Not medical advice.
Planning meals? Try the Macro Calculator or Calorie Calculator.
Pick a fasting plan like 16:8, 18:6 or OMAD, enter when you finish your last meal, and see when your fast ends, your eating window, and your fat-burning milestones.
About this Intermittent Fasting Calculator
The Intermittent Fasting Calculator builds your daily fasting schedule. Pick a plan — 12:12, 14:10, 16:8, 18:6, 20:4 or OMAD — enter when you finish your last meal, and see exactly when your fast ends, when your eating window opens and closes, and when you reach milestones like fat burning and ketosis. Download it as a printable PDF schedule.
What you'll need
- • Fasting plan (16:8, 18:6, 20:4, OMAD…)
- • Time you finished your last meal
How it works
- 1. Choose your fasting plan.
- 2. Enter the time you finished your last meal.
- 3. Read your fast end time and eating window.
- 4. Check the fat-burning and ketosis milestones.
- 5. Tap PDF to download your printable schedule.
Worked example
18:6 starting at 7:00 PM: the fast ends at 1:00 PM the next day and you eat between 1:00 PM and 7:00 PM.
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Intermittent Fasting Calculator FAQ
What is the Intermittent Fasting Calculator?
The Intermittent Fasting Calculator is a free online tool that helps you fasting end time, eating window, and milestones for 16:8, 18:6 or omad.
How do I use the Intermittent Fasting Calculator?
Open the Intermittent Fasting Calculator, enter the requested values, and review the instant estimate on the page.
Is the Intermittent Fasting Calculator free?
Yes. The Intermittent Fasting Calculator is free to use on Fast Online Calculator and does not require an account.
What is 16:8 intermittent fasting?
You fast for 16 hours and eat during an 8-hour window each day — for example, eating from noon to 8 PM.
What does OMAD mean?
One Meal A Day — about a 23-hour fast with a 1-hour eating window.
When does fat burning start while fasting?
For many people the body shifts toward burning fat around 12 hours after the last meal, and early ketosis can begin around 16 hours. It varies by person.
Can I drink coffee while fasting?
Black coffee, plain tea and water have almost no calories and are usually allowed. Milk, sugar and creamer break a strict fast.
Is intermittent fasting safe?
It is safe for many healthy adults, but talk to your doctor first if you are pregnant, diabetic, underweight, or take medication.
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