GPS week and day of year (DOY): GNSS calendar and date converter
Converts dates to GPS week, day of year (DOY), seconds of week and Julian date/MJD, and back. With a monthly GPS calendar and a live GPS clock. It is what you need to find RINEX files, ephemerides and IGS products.
The time only changes the result near midnight (the GPS day and the DOY are counted in UTC) and in the seconds of week.
Weeks are counted from January 6, 1980. If your receiver shows the short 10-bit week (0 to 1023), add 2048 (for dates after April 2019) — typing the short week here works too, the calculator adds it for you. The IGS file format is also accepted: 24383 (week + day).
The DOY is part of RINEX file names (e.g. algo2700.26o = day 270 of 2026).
Result
GPS calendar
Each cell shows the date and, below it, the day of year. On the left, the GPS week (which starts on Sunday). Click a day to convert it.
GPS week, day of year and GPS time
The GPS week counts weeks since January 6, 1980 and always starts on Sunday (day 0) at midnight GPS time. The seconds of week (time of week, TOW) run from 0 to 604,799. The day of year (DOY) runs from 1 to 365 (366 in a leap year) and is counted in UTC.
GPS time has no leap seconds: today it is 18 seconds ahead of UTC (since 2017). For older dates, the calculator uses the offset that was in force at the time. The short week some receivers show (0 to 1023) is the same count, rolled over every 1024 weeks.
FAQ
What GPS week is it now?
The “Now” box at the top shows the current GPS week, day of week, day of year and GPS time, updated every second.
What is the day of year (DOY) used for?
RINEX files from the IGS and from national CORS/GNSS networks are organized by year and day of year. E.g. algo2700.26o (RINEX 2) and ALGO00CAN_R_20262700000_01D_30S_MO.crx.gz (RINEX 3) are day 270 of 2026 at station ALGO. Use the DOY to find the right folder and file on the data servers.
On which day does the GPS week start?
On Sunday, at 00:00 GPS time (day 0). Saturday is day 6. Older IGS product names use the week + day format (e.g. igs21000.sp3).
What is the difference between GPS time and UTC?
GPS time has been 18 s ahead of UTC since January 1, 2017, because it does not get leap seconds. In 1980, when GPS time started, they were equal.
What is the GPS week rollover?
The legacy GPS navigation message broadcasts the week number in 10 bits (0 to 1023). The count rolled over to zero in August 1999 and in April 2019; older receivers may show wrong dates because of it. Here the week is always shown in full and also in the short (10-bit) form.