Spring ahead and Fall back.

Discover when and where people observe Daylight Saving Time and Summer Time, and when you should switch your clocks.

Easy and fun.

Twirl the globe, zoom in with a pinch, and tap on a country. Or type in a country name. You’ll learn whether or not that country observes Daylight Saving Time, and if so, what date and time it will start or end during any given year.

Share the dates!

You can remind others to spring ahead or fall back thanks to the app’s full integration with email, Facebook, and Twitter. On the iPhone, you can also set calendar alerts for a given country, choosing from among the next time change only, the changes this year, or the next decade of time changes, and send text messages.

History and intrigue.

Explore the rationale behind Daylight Saving Time, its history, and its unintended consequences. Does having more daylight in the evening really save energy? How can Daylight Saving Time switch the birth order of twins? How did Daylight Saving Time thwart would-be terrorist bombers?