# Time zone math
**URL:** https://boards.straightdope.com/t/time-zone-math/620330
**Category:** Factual Questions
**Created:** [April 29, 2012, 4:37pm UTC](https://boards.straightdope.com/t/time-zone-math/620330 "2012-04-29T16:37:34Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@toadspittle](https://boards.straightdope.com/u/toadspittle)
#### Post date: [April 29, 2012, 4:37pm UTC](https://boards.straightdope.com/t/time-zone-math/620330/1 "2012-04-29T16:37:34Z")
Sorry for what may seem a really dumb question, but I don’t want to get this wrong…
I’m looking to book a flight from the West Coast of the US to Hong Kong.
The flight leaves at 1:50PM PT on October 16.
The (13-hour-long) flight arrives at 5:55PM HKT … but on what day?
One booking site tells me simply “This is an overnight flight.”
Another says, “October 16 +1 day.”
But… aren’t we across the International Date Line? Shouldn’t it be +2 days?
Just staying on PT (in 24-hr time), 10/16 13:50 + 13:05 hours = 10/17 2:55.
So shouldn’t the arrival be on 10/18?
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### Author:  [@hibernicus](https://boards.straightdope.com/u/hibernicus)
#### Post date: [April 29, 2012, 4:42pm UTC](https://boards.straightdope.com/t/time-zone-math/620330/2 "2012-04-29T16:42:34Z")
17th. Forget about the dateline and add the number of hours time difference as if you were travelling east.
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### Author:  [@ads95](https://boards.straightdope.com/u/ads95)
#### Post date: [April 29, 2012, 4:47pm UTC](https://boards.straightdope.com/t/time-zone-math/620330/3 "2012-04-29T16:47:31Z")
Depart from West Cost at 1:50pm on October 16. Flight is 13 hours. Therefore, flight arrives at 2:50am October 17 West Coast Time.
Hong Kong is 15 hours ahead of West Coast Time Zone
Therefore, at 2:50am October 17 on the West Coast, it is 5:50pm in Hong Kong on October 17.
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### Author:  [@toadspittle](https://boards.straightdope.com/u/toadspittle)
#### Post date: [April 29, 2012, 5:35pm UTC](https://boards.straightdope.com/t/time-zone-math/620330/4 "2012-04-29T17:35:00Z")
Thank you. I was getting confused after a trip I made to NZ, where I lost an entire day in one direction (i.e., went from something like May 2 to May 4 without experiencing the 3rd…).