Intermittent fasting calculator
Choose a schedule and the time of your first meal to see when your eating window opens and closes.
Loading the calculator
What your result means
On a time-restricted schedule such as 16:8, you eat only inside a daily window and fast for the rest of the day. The first number is the hours you fast and the second is the hours you eat. The result shows when each window starts and ends.
OMAD (one meal a day) is a one-hour eating window followed by 23 hours of fasting. It is the most demanding of these schedules and makes it harder to eat enough protein and nutrients.
5:2 works by the week, not the hour. You eat as usual on five days and eat much less on two non-consecutive days, commonly 500 to 600 calories.
How it's calculated
Formula
- Eating window end = first meal time + eating hours
- Fasting window = the remaining hours, from the end of the eating window to the next first meal
- Eating hours: 16:8 is 8 hours, 18:6 is 6 hours, 20:4 is 4 hours, OMAD is 1 hour
- 5:2: five regular days and two low-calorie days a week, no daily window
Times use a 24-hour clock. A window that passes midnight ends on the next day.
Intermittent fasting is one way to eat less overall, not a requirement for weight loss. Research suggests it can help some people but is not better for everyone than other approaches.
Sources
Learn more in the Academy
Frequently asked questions
Water is fine. Many people also have plain black coffee or unsweetened tea. Anything with calories, including milk and sugar, ends the fast.
Most people start with 16:8 because it fits around normal meals. Move to a longer fast only if you feel well and are meeting your nutrition needs.
Some people do, some feel better with a meal before training. Listen to how you feel, drink water, and stop if you feel dizzy or unwell.
Fasting is not suitable for everyone. Avoid it if you are pregnant or breastfeeding, have diabetes, have a history of eating disorders, or are under 18, and speak to a doctor first if you have any medical condition.
Calculators give estimates for healthy adults and are not medical advice. Talk to a qualified professional before changing your training or nutrition, especially if you have a health condition.
Track this in Atlas
Log your food and training in Atlas and keep your targets in one place.
Coming soon
