Intermittent Fasting Calculator
Plan your intermittent fasting schedule in seconds. Choose a protocol and when your last meal ends to see your daily eating window, when your fast breaks, and a printable 7-day schedule.
Last updated:
Typically 500 for women, 600 for men
How to use the Intermittent Fasting Calculator
- Choose a protocol, for example 16:8 for 16 hours fasting and an 8-hour eating window.
- Enter when your last meal ends, such as 8:00 PM.
- Pick a start date and 12- or 24-hour time.
- Read your eating window and when each fast ends.
- Download the weekly schedule as CSV or copy the result.
How the eating window is calculated
For daily protocols, the calculator works backwards from the time your last meal ends:
- Eating window start = last meal time − eating hours
- Fast = 24 h − eating hours, from your last meal until the next day's first meal
Example (18:6): last meal ends 7:00 PM → eating window 1:00 PM – 7:00 PM, fast 7:00 PM to 1:00 PM next day (18 hours).
Intermittent fasting protocols compared
| Protocol | Fast | Eating window | Example window | Difficulty |
|---|---|---|---|---|
| 12:12 | 12 h | 12 h | 7 AM – 7 PM | Easy |
| 14:10 | 14 h | 10 h | 9 AM – 7 PM | Easy |
| 16:8 | 16 h | 8 h | 12 PM – 8 PM | Moderate |
| 18:6 | 18 h | 6 h | 1 PM – 7 PM | Harder |
| 20:4 | 20 h | 4 h | 3 PM – 7 PM | Hard |
| OMAD (23:1) | 23 h | 1 h | 6 PM – 7 PM | Very hard |
| 5:2 | 2 low-calorie days | 5 normal days | Mon & Thu ≈ 500–600 kcal | Moderate |
Tips: keep the same window every day so your body adapts, drink plenty of water, and make the meals in your window nutritious. If you feel unwell, shorten the fast. Check with a doctor first if you have a medical condition.
Frequently asked questions
How does the 16:8 schedule work?
You fast for 16 hours and eat within an 8-hour window each day. If your last meal ends at 8:00 PM, your eating window is 12:00 PM to 8:00 PM and you fast from 8:00 PM until noon the next day. Sleep covers a large part of the fast.
What can I have during the fast?
Most plans allow water, plain black coffee and unsweetened tea, since they have almost no calories. Anything with meaningful calories, such as milk, juice or snacks, breaks the fast.
Which intermittent fasting protocol should a beginner choose?
Many people start with 12:12 or 14:10 and move to 16:8 after a week or two once the shorter fasts feel comfortable. 18:6, 20:4 and one meal a day are more demanding.
What is the 5:2 diet?
You eat normally five days a week and reduce intake to about 500 calories (women) or 600 calories (men) on two non-consecutive days, such as Monday and Thursday.
Does intermittent fasting help with weight loss?
It can, mainly because a shorter eating window often leads to eating fewer calories. Studies generally find results similar to ordinary calorie restriction, so food quality and total intake still matter.
Who should not try intermittent fasting?
It is not recommended for children and teens, during pregnancy or breastfeeding, for people with a history of eating disorders, or for people with diabetes or other conditions who take medication, unless a doctor supervises it.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.