Daylight saving time and travel
Why end times can shift by an hour when the clocks change, and how to handle trips across time zones.
Talk with a healthcare professional before changing how you eat if you have a medical condition, take medication, are pregnant or breastfeeding, are under 18, or have a history of disordered eating. Stop and seek help if you feel unwell.
Elapsed time vs clock time
The timer and schedule calculator count real elapsed hours. Most of the time, elapsed hours and clock time agree: 20:00 plus 16 hours is 12:00 the next day. On the two nights a year when clocks change, they do not. The tools always keep the elapsed hours correct, so the clock time at the end can look one hour different from simple addition.
When the clocks go forward
In spring, clocks jump forward one hour overnight, so that night has only 23 hours. A 16-hour fast starting at 20:00 the evening before ends at 13:00 by the clock, not 12:00, because the hour from 02:00 to 03:00 is skipped.
When the clocks go back
In autumn, clocks go back one hour, so that night has 25 hours. A 16-hour fast starting at 20:00 ends at 11:00 by the clock, not 12:00, because the hour from 01:00 to 02:00 happens twice.
| Night | Start | Duration | Clock time at end |
|---|---|---|---|
| Normal night | 20:00 | 16 hours | 12:00 |
| Clocks go forward | 20:00 | 16 hours | 13:00 |
| Clocks go back | 20:00 | 16 hours | 11:00 |
In Canada and the United States, daylight saving time usually starts on the second Sunday in March and ends on the first Sunday in November. Dates differ in other countries, and some places do not change their clocks at all.
Travelling across time zones
Your device shows times in its current time zone. If you start a timer in Winnipeg and land in Vancouver, the elapsed time is unchanged, but the start and end are shown in Vancouver time, two hours earlier by the clock. Eastbound trips make the clock time later.
- Long flights disrupt sleep and meals. Many people find it easier to set fasting plans aside on travel days and eat according to local meal times on arrival.
- Stay hydrated on flights; cabin air is dry.
- If you take medicines on a schedule, ask your pharmacist how to adjust the timing across time zones.
Planning tips
On a clock-change weekend, use the schedule calculator to see the exact end time; it accounts for the change automatically on your device. For a trip, plan the days after arrival in the weekly planner once your device has switched to the local time zone.
Reviewed October 2026 by Lee Palmer · How we write our guides · Report an error