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How to use the fasting calculator
- Pick a schedule. The numbers are fasting hours and eating hours.
- Choose how to plan it. Start from your first meal (handy if you skip breakfast) or from your last meal (handy if you want to stop eating by a set time).
- Set the time. The 24-hour clock shows your eating window in orange, your fasting window in the background, and a marker for the current time.
The schedules
| Schedule | Fasting | Eating | Example eating window |
|---|---|---|---|
| 12:12 | 12 hours | 12 hours | 8 am to 8 pm |
| 14:10 | 14 hours | 10 hours | 9 am to 7 pm |
| 16:8 | 16 hours | 8 hours | Noon to 8 pm |
| 18:6 | 18 hours | 6 hours | 1 pm to 7 pm |
| 20:4 | 20 hours | 4 hours | 3 pm to 7 pm |
| One meal a day | 23 hours | 1 hour | 6:30 pm to 7:30 pm |
Windows can cross midnight; the calculator handles that and labels the next day.
What the research says
Intermittent fasting is popular, and the evidence is more modest than the hype:
- The window alone isn’t magic. In the TREAT randomized trial, adults who ate only between noon and 8 pm for 12 weeks didn’t lose significantly more weight than a group eating three structured meals a day. The authors concluded that time-restricted eating on its own was not more effective than eating throughout the day.
- Calories still decide. In a 12-month trial in people with obesity, everyone followed the same calorie target; adding an 8 am to 4 pm eating window didn’t produce a significantly different weight loss than calorie restriction alone.
- It’s an active research area. A review in The New England Journal of Medicine describes the metabolic changes that fasting periods can trigger and the open questions that longer human studies still need to answer.
The practical takeaway: fasting can be a useful structure if it makes eating within your calorie target easier. If it makes you ravenous, grumpy or preoccupied with food, a regular meal pattern works just as well.
Tips for a comfortable fast
- Start gently. Begin with 12:12 or 14:10 and lengthen the fast only if it feels good.
- Make the first meal count. Opening with protein and fiber keeps you fuller for longer.
- Drink water. Water, plain coffee and plain tea are fine during the fasting window.
- Keep the window steady. A similar window on most days, weekends included, is easier than a different plan every day.
- Fit training around it. Many people who train hard prefer to do it inside or just before their eating window.
Who should be careful
Fasting isn’t suitable for everyone. Skip it, or talk to your doctor first, if you’re pregnant or breastfeeding, under 18, have had an eating disorder, have diabetes or take medication that lowers blood sugar or must be taken with food.
Tracking your fasts in Calorix
Calorix’s fasting tracker supports 12:12, 14:10, 16:8, 18:6, 20:4, one meal a day and custom windows. Start and stop the timer in one tap, follow it on your Lock Screen with a Live Activity, and get a reminder when your window opens or closes. Toasty naps while you fast and wakes up when it’s time to eat. Your food log and your fasts live in the same place, so you can see both at a glance. Read more about the intermittent fasting tracker or our 16:8 guide.
Updated October 9, 2026
