Upcoming GPS Week Number Rollover Event

News | 11 March 2019

The Global Positioning system (GPS) provides date and time of day in the form of a number of weeks from a start date and the number of seconds within a week. GPS receivers can translate this information into a normal date and time display.


The week count is a 10-bit parameter meaning it ‘rolls over’ from 1023 to 0 every 19.7 years when a new GPS ‘epoch’ begins. The GPS week number first rolled over in 1999 and the next rollover will happen just before midnight (UTC) on 6th April 2019. Depending on how your GPS receiver handles this rollover it may give an incorrect date. The problem is more likely to occur with older GPS equipment, newer receivers which conform to the latest IS-GPS-200 specification should not be adversely affected.

This problem is specific to GPS. Those satellite navigation systems developed after GPS, such as the Russian GLONASS, European Galileo or Chinese BeiDou, are not affected by this problem.

In the future GPS will use a 13-bit week number, making the GPS epoch 157 years, so GPS week number rollover will, for all practical purposes, no longer be a problem.

How a receiver uses the information in the transmitted GPS message to determine date and time, and therefore the impact (if any) of the week number rollover event, is manufacturer-specific. Users of GPS are therefore advised to consult the device manufacturer in the first instance if they have concerns.

For more information:

http://www.npl.co.uk/science-technology/time-frequency/time/faqs/when-and-what-is-the-gps-week-rollover-problem-(faq-time)(external link)

https://en.wikipedia.org/wiki/Global_Positioning_System#Format(external link)

and the links in this document from Homeland Security [PDF, 212 KB]