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GPS Week Number Rollover

The GPS Week Number count began at approximately midnight on the evening of 05 January 1980 / morning of 06 January 1980. Since that time, the count has been incremented by 1 each week, and broadcast as part of the GPS message. The GPS Week Number field is modulo 1024. This means that at the completion of week 1023, the GPS week number rolled over to 0 on midnight GPS Time of the evening of 21 August 1999 / morning of 22 August 1999. Note that this corresponded to 23:59:47 UTC on 21 August 1999.


Week beginning
at 0000 GPS Time on

GPS Week Number
broadcast by satellites

08 Aug 1999 1022
15 Aug 1999 1023
22 Aug 1999 0
29 Aug 1999 1
24 Mar 2019 1022
31 Mar 2019 1023
07 Apr 2019 0
14 Apr 2019 1


It is the responsibility of the user (i.e., user equipment or software) to account for the previous 1024 weeks.

Depending upon the manufacturer of your GPS receiver, you may or may not have been effected by the GPS Week Number Rollover on 22 August 1999. Some receivers may display inaccurate date information, some may also calculate incorrect navigation solutions.

Contact the manufacturer of your GPS receiver if you have been effected by the GPS week number rollover. Contacts for some GPS receiver manufacturers can be found at the GPS World website.

For more information, please refer to the following websites:

USNO Master Clock Time
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