Guide
Converting GPS week and time of week to UTC
Satellite navigation receivers, drone flight logs, survey equipment and RINEX observation files often record time not as a date but as a GPS week number and a time of week in seconds. Turning that into a calendar date needs three pieces of knowledge: the GPS epoch, the leap seconds that UTC has added since, and whether the week number has rolled over. This converter handles all three.
How GPS counts time
GPS time started at 00:00:00 UTC on 6 January 1980, a Sunday. It is counted in weeks since that moment and seconds within the current week, from 0 at Sunday midnight to 604,799 just before the next. Week 0 began on the epoch; the current weeks number well over two thousand. Some software uses a single count of seconds since the epoch instead, which is the second input mode.
Why GPS runs ahead of UTC
UTC occasionally inserts a leap second to stay close to the Earth’s rotation; GPS time never does. Each leap second since 1980 has therefore put GPS one second further ahead. Eighteen have been added, the last at the end of 2016, so GPS time is now 18 seconds ahead of UTC. The converter applies the leap seconds that had occurred by the date in question, so older timestamps use smaller offsets.
The 10-bit week rollover
The original GPS navigation message transmits the week number in only 10 bits, so it counts from 0 to 1,023 and then wraps to zero again, every 1,024 weeks, or about 19.6 years. Rollovers happened in August 1999 and April 2019. Receivers and logs that report only those 10 bits need the missing rollovers added back, which is what the rollover menu does; forgetting it shows dates about 19.6 years in the past. The output shows each date’s 10-bit week and rollover count.
Three ways in
Enter a week and time of week, a total number of GPS seconds, or a UTC date and time. Whichever you start from, the panel shows the UTC and local date, Unix time, the full GPS week, the time of week with the day of the week it falls on, total GPS seconds, the 10-bit form and the leap-second offset.
A worked example
The Sample is GPS week 2391 with a time of week of 432,018 seconds. That is 2025-11-07T00:00:00.000Z: 432,018 seconds is five days and 18 seconds into a week that began on Sunday 2 November, and subtracting the 18 leap seconds lands exactly on Friday midnight UTC. As a 10-bit value, the week is 343 in rollover 2.
Time of week tips
Day 0 is Sunday, so tow ÷ 86400, rounded down, gives the weekday. Receivers often report time of week with a fraction of a second, which the converter accepts to the millisecond. If a week number looks too small for a recent log, it is almost certainly a 10-bit value.
Leap-second limits
The leap-second table ends with the one added on 31 December 2016; none has been scheduled since, and the international timekeeping community has decided to stop adding them by 2035. If one were ever added, dates after it would be off by a second here until the table was updated. Dates before 6 January 1980 have no GPS representation and are flagged.
Related tools
- Timestamp Converter converts the resulting Unix time.
- LDAP / FILETIME Converter handles Windows timestamps.
- Cocoa Timestamp Converter reads Apple timestamps.
- Time Zone Converter shows the UTC time in other zones.
Checked against the current version of the GPS Time Converter on .