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'EST' and 'EDT' Are Different Time Zones

A man changes the time on an old-fashioned train station clock
Credit: FPG / Staff - Getty Images

This year, Daylight Saving Time starts on March 14 and lasts all summer—and if you don’t commit that fact to memory you will one day screw up something time zone related. So, remember: summer is daylight time (EDT if you’re on the east coast) and winter is standard time (EST).

Same deal in other parts of the continent: pacific time is PST in the winter, PDT in the summer. Mountain time has MST and MDT, central has CST and CDT. You get the idea.

Please don’t schedule a virtual meeting with an overseas colleague this summer by saying you’re free at such-and-such time “EST.” You’re not—and if they plug Eastern Standard Time into a time zone calculator, they may end up confirming the meeting for a time that isn’t the one you meant.

Fortunately, many time zone tools are smart enough to know when it’s standard time and when it’s daylight time, and will fix your mistake (like this one). But if you don’t know the difference, you’re vulnerable to screwups when:

  • Your location has switched from standard to daylight time (or vice versa) but the other person’s hasn’t. The dates for switching over aren’t the same worldwide. For example, the U.S. has daylight savings from March 14 to November 7this year, but the UK has it from March 28 to October 31. During those in-between times, you have to be extra careful that you’re converting correctly.

  • You’re scheduling something for the future. Perhaps it’s daylight time now, but it will be standard time by the time the appointed day arrives. Better double check that anybody coming from a different time zone gets the right time on their calendar.

  • You’re dealing with a program that doesn’t account for your ignorance. Many tools are smart enough to adjust automatically, but some aren’t. If you pick “EST” off a menu when you’re scheduling a reminder or an automated event, but your actual time is EDT, the computer will do its thing an hour too late.

If you truly want to remain clueless, it’s fine to say “ET” or “eastern time” (likewise for CT, MT, and PT); do so, and you’re just being imprecise, not wrong. Or give the name of a nearby city: “America/New York” and “America/Los Angeles” are options in every time zone menu. But if you go to the trouble of providing your three-letter time zone abbreviation, make sure you know which is which.

This post was originally published in May 2018 and updated on March 9, 2021 to change the header photo and provide additional context for 2021.