What is the GPS epoch?

The GPS epoch is midnight (00:00:00 UTC) at the start of Sunday, January 6, 1980. All GPS week numbers and second-of-week values are counted from this moment. GPS week 0 started on January 6, 1980.

What is the GPS week rollover?

Early GPS receivers store the week number in a 10-bit field, which can hold values 0 through 1023. After week 1023 the counter wraps back to 0. This rollover has occurred twice: on August 21, 1999 (end of cycle 0) and April 6, 2019 (end of cycle 1). The next rollover is November 20, 2038 (end of cycle 2).

What is the day of week in GPS time?

GPS days of week are numbered 0 (Sunday) through 6 (Saturday), matching the start of the GPS epoch which was a Sunday. Day 0 always begins at 00:00:00 GPS time on Sunday.

What is the second of week?

The second of week (SOW) counts elapsed seconds since the start of the current GPS week. It runs from 0 at midnight Sunday to 604 799 at the end of Saturday. Many GPS protocols (e.g., RINEX) use SOW to timestamp observations.

Does GPS time account for leap seconds?

No. GPS time does not include leap seconds. As of 2024, GPS time is 18 seconds ahead of UTC. This tool displays results in GPS time and provides the equivalent UTC time using the current leap-second offset. For highest accuracy in historical conversions, verify the leap-second count in effect at that date.

What is the full (unrolled) GPS week number?

The full GPS week is the total count since the epoch without wrapping, currently in the 2300s range. The truncated (modular) week is what a 10-bit receiver transmits (0–1023). This tool shows both.

GPS Week Converter

Name: GPS Week Converter
Availability: InStock
Author: Nham Vu

Convert between GPS week number plus day-of-week and calendar dates, with full rollover cycle awareness since the GPS epoch of January 6, 1980.

GPS Week Number

Full or truncated (0–1023)

Day of Week

Hour (GPS/UTC)

Minute

Second

Rollover cycle (for truncated week numbers)

Auto-detect Cycle 0 (pre-1999) Cycle 1 (1999–2019) Cycle 2 (2019–2038)

Enter GPS week or calendar date and click Convert.

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Summary

Convert between GPS week number plus day-of-week and calendar dates, with full rollover cycle awareness since the GPS epoch of January 6, 1980.

How it works

Select the conversion direction: GPS week to calendar date, or calendar date to GPS week.
For GPS-to-date: enter the GPS week number, the day of week (0 = Sunday, 6 = Saturday), and the time of day in UTC.
For date-to-GPS: enter the calendar date and UTC time.
The tool computes the elapsed days since the GPS epoch (January 6, 1980) and derives the GPS week, day, and second-of-week.
The rollover cycle number (0, 1, 2, …) is shown so you can interpret legacy GPS receivers that transmit only 10-bit week numbers.
Results include the full GPS week number, the day of week, the second of week, and the equivalent UTC calendar date and time.

Use cases

Decode GPS timestamps from raw receiver output or NMEA sentences.
Convert archived GPS log files that store data as week + second-of-week.
Verify that a GPS receiver has correctly handled the 1024-week rollover.
Calculate the GPS week for a specific mission date in satellite geodesy.
Check when the next GPS week rollover will occur.
Debug time-stamp mismatches in GPS-synchronized survey equipment.
Convert GPS time to UTC for scientific data publications.
Understand the GPS time scale for navigation and timing applications.

Frequently Asked Questions

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Last updated: 2026-05-29 · Reviewed by Nham Vu