resetA fasting schedule describes a division of time. The first number is the fasting window; the second is the eating window. For daily schedules, the two add up to 24 hours. The numbers do not describe calories, a meal plan or a guaranteed health result.
Read the numbers before choosing a routine
In a 12:12 schedule, each window is 12 hours. In 14:10, the fasting window is 14 hours and the eating window is 10. In 16:8, they are 16 and eight hours respectively. Sleep falls inside a fasting window if the window runs overnight; you do not add sleeping hours a second time.
The table below is arithmetic, not a recommendation. Every example starts at the same time so you can see the difference clearly.
| Schedule | Last meal ends | Fasting window ends | Eating window |
|---|---|---|---|
| 12:12 | 20:00 | 08:00 next day | 08:00–20:00 |
| 14:10 | 20:00 | 10:00 next day | 10:00–20:00 |
| 16:8 | 20:00 | 12:00 next day | 12:00–20:00 |
Use the schedule calculator to move these examples around your day. It calculates a regular 24-hour cycle, without adjusting for daylight-saving changes or travel.
A time that fits is only part of the decision
Work, family meals, sleep and exercise can all affect how practical a schedule feels. A timetable that is convenient is not necessarily medically appropriate. A timer cannot assess your nutritional needs, medication or health history.
There is no need to treat the numbers as levels to progress through. Finishing a longer window is not a measure of personal success. If you and your clinician decide to use a fasting routine, choose the timing deliberately and be willing to change it.
Before you start
Speak with a qualified clinician before changing how you eat. Fasting is not suitable for everyone. Johns Hopkins Medicine identifies children and teenagers under 18, people who are pregnant or breastfeeding, people with type 1 diabetes taking insulin, and people with a history of eating disorders as groups who should avoid intermittent fasting. Read its overview and safety guidance.
If you have diabetes or take medication, ask your clinician about your individual risks; do not change a prescription to fit a schedule. The US National Institute of Diabetes and Digestive and Kidney Diseases explains why fasting and diabetes require individual clinical assessment.
This guide explains schedule notation and app use. It is not a personalised fasting plan or medical advice, and it has not been medically reviewed.
Put the record in context
Reset lets you choose a preset or a custom target and shows time remaining. If you begin the timer late, correct the actual start time instead of letting the record become inaccurate. If you end earlier than planned, keep the honest entry. Learn how to edit and log a fast.
The timer is a record of elapsed time. The educational timeline is not a reading from a sensor, a blood test or a measurement of your metabolism. That distinction stays important whatever window you choose.