GPS time is represented by a week number and a number counting seconds into the week. The week counter is stored as a 10-bit number; meaning the value of the week number field can be between 0 and 1023.
On April 6th, the week’s field number will have reached 1023, and will roll over from 1023 to 0. Depending on the manufacturer of the GPS receiver, or versions of firmware, a GPS receiver may be affected by this roll over.
GPS Clocks may display inaccurate date and time information, such as rolling time back to the previous Epoch (August 21, 1999), and GPS Navigation Systems may be affected.
The GPS week counter started at 0 on January 6th, 1980. Since then, the week counter has reached its maximum and been reset once, last occurring on August 21, 1999. The next occurrence of the GPS week rollover for GPS clocks with 10-bit week numbers following April 6th 2019 will be November 20, 2038.
Modernised GPS clocks, and GPS navigation systems may be released with a 13-bit week field, allowing up to 8192 weeks, instead of 1023 weeks, before rolling over to 0. This will increase the time between GPS week roll overs from approximately 20 years, to around 150 years.