About the Intermittent Fasting Calculator
What is the Intermittent Fasting Calculator?
Choose a fasting schedule and your first meal time, and this intermittent fasting calculator gives your eating window and when the fast begins.
It also spaces your meals across the window and splits your calories between them.
How to use the Intermittent Fasting Calculator
- Fasting Schedule (sample: 16:8 (most popular))
- First Meal At (sample: 12:00)
- Meals in the Eating Window (sample: 2)
- Daily Calories (normal days) (sample: 1,800)
- Sex (for 5:2 fast-day calories) (sample: Female)
- Press Plan Fasting Window (results also refresh as you type). The result card shows the Eating Window, along with Fast starts, Fasting hours per day, Fasting hours per week and Suggested meal times.
Formula used
Window end = First meal + (24 − Fasting hours)
For 5:2, fast days are about 500 kcal for women and 600 kcal for men.
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| Fasting Schedule | 16:8 (most popular) |
| First Meal At | 12:00 |
| Meals in the Eating Window | 2 |
| Daily Calories (normal days) | 1,800 |
| Sex (for 5:2 fast-day calories) | Female |
| Result | Value |
|---|---|
| Eating Window | 12:00 PM – 8:00 PM |
| Fast starts | 8:00 PM (after your last bite) |
| Fasting hours per day | 16 |
| Fasting hours per week | 112 |
| Suggested meal times | 12:00 PM, 7:30 PM |
| Calories per meal | 900 kcal |
| During the fast | Water, black coffee or plain tea without sugar or milk |
| Caution | Not advised in pregnancy, for children, with a history of eating disorders, or with diabetes medication without a doctor's advice |
Tips for using the Intermittent Fasting Calculator
- Start with 12:12 or 14:10 and extend gradually.
- Break your fast with protein and vegetables rather than sweets.