EST vs EDT and PST vs PDT: What the Letters Mean
EST and PST are the winter names for US Eastern and Pacific time, and EDT and PDT are the summer names, one hour ahead, used while daylight saving is on. The zones themselves never move; only the label and the offset change with the season.
What the letters mean
| Zone | Winter name | Offset | Summer name | Offset |
|---|---|---|---|---|
| Eastern | EST (Standard) | UTC-05:00 | EDT (Daylight) | UTC-04:00 |
| Central | CST | UTC-06:00 | CDT | UTC-05:00 |
| Mountain | MST | UTC-07:00 | MDT | UTC-06:00 |
| Pacific | PST | UTC-08:00 | PDT | UTC-07:00 |
The middle letter gives it away: S for Standard time, D for Daylight time.
When the US switches
Clocks go forward an hour at 2:00 AM on the second Sunday in March and back an hour at 2:00 AM on the first Sunday in November. Hawaii and most of Arizona (everywhere except the Navajo Nation) stay on standard time all year. Other countries use different dates, which how daylight saving time works lays out.
So in practice it's EDT from March to November and EST for the rest of the year.
EST or ET: which should you write?
We'd write ET and PT almost every time. They mean whatever Eastern or Pacific time is in force, so you never end up writing EST in July, which is technically an hour wrong. Save EST or EDT for the rare times you really mean that exact offset.
EST vs PST
Pacific is three hours behind Eastern all year round, because both zones change on the same day. 12:00 noon EST is 9:00 AM PST, and 12:00 noon EDT is 9:00 AM PDT. You can try any time on the EST to PST page.
Adding India or the UK to the mix
This is where it gets fiddly, because India never changes its clocks and the UK changes on different dates from the US. From New York, India is 10 hours 30 minutes ahead in winter and 9 hours 30 minutes ahead in summer. The details, with a table, are in IST to EST: how to convert.