GPS Time Converter

A GPS time converter translates between GPS time (the continuous count of weeks and seconds since January 6, 1980) and standard UTC/Gregorian calendar dates. You enter a GPS week and seconds-of-week (or a UTC date), and the calculator returns the corresponding date/time in the other format, accounting for leap seconds.

Formula

GPS time is a continuous count of seconds since the GPS epoch: January 6, 1980, 00:00:00 UTC (which was a Sunday). The formula to convert GPS week and seconds-of-week to a UTC date is:

UTC time = GPS epoch + (GPS week × 7 × 86,400) + GPS seconds-of-week − leap seconds

Where:

• GPS week – the integer week number since the epoch (0 = first week).
• GPS seconds-of-week – the number of seconds since the start of the current GPS week (0 to 604,799).
• 7 × 86,400 – the number of seconds in one week (604,800).
• Leap seconds – the cumulative number of leap seconds inserted into UTC since 1980. As of mid-2024, this is 18 seconds.

To convert a UTC date to GPS time, reverse the process: subtract the GPS epoch, then add leap seconds, and divide the total seconds by 604,800 to get weeks and remainder seconds.

Worked Example

Using the calculator’s defaults: GPS week 2245, seconds-of-week 345,600 (which is 4 days into the week, i.e., Thursday).

1. Total seconds since GPS epoch = 2245 × 604,800 + 345,600 = 1,357,776,000 + 345,600 = 1,358,121,600 seconds.
2. Convert to days: 1,358,121,600 ÷ 86,400 = 15,718 days (exact).
3. Add to GPS epoch (Jan 6, 1980): 15,718 days later is February 1, 2023 (you can verify with a date calculator).
4. Subtract 18 leap seconds: February 1, 2023, 00:00:00 UTC minus 18 seconds = January 31, 2023, 23:59:42 UTC.

The calculator’s first output shows the UTC date/time as 2023-01-31 23:59:42, matching the example. The second output shows the GPS date/time (without leap seconds) as 2023-02-01 00:00:00, which is the raw GPS time.

Why GPS Time Exists

GPS satellites carry highly accurate atomic clocks, and the system needs a single, continuous time scale that doesn’t skip seconds. UTC, the standard civil time, is occasionally adjusted by leap seconds to keep Earth’s rotation in sync. GPS time ignores those adjustments, so it runs continuously and is easier for navigation and timing calculations. The GPS epoch was chosen to align with UTC at the start of 1980, but since then leap seconds have caused a growing offset (currently 18 seconds).

How to Read the Results

When you convert GPS time to UTC, the result is the exact civil time you’d see on a clock, including the leap-second offset. When you convert UTC to GPS time, you get the week number and seconds-of-week that a GPS receiver would report. The seconds-of-week always ranges from 0 to 604,799, and the week number increases every Sunday at midnight GPS time. If you’re working with a GPS receiver, it typically outputs both week number and seconds-of-week, so this converter helps you interpret those numbers.

Common Mistakes and Pitfalls

• Forgetting leap seconds – Always subtract the current leap-second offset when going from GPS to UTC, and add it when going the other way. The offset changes occasionally (last added in 2017).
• Week rollover – GPS week numbers roll over every 1,024 weeks (about 19.7 years). The first rollover occurred in 1999, the second in 2019. Some receivers may report week numbers modulo 1,024, so add 1,024 or 2,048 to get the correct epoch.
• Seconds-of-week range – Valid values are 0 to 604,799. Values outside this range are invalid, though some systems allow negative or >604,799 to represent adjacent weeks.
• Time zone confusion – GPS time is always UTC-based; it does not have a time zone. When converting to local time, apply your time zone offset after the UTC conversion.

Alternatives and Related Time Scales

Besides GPS time, there are other time scales you may encounter:

• UTC (Coordinated Universal Time) – The civil time standard, adjusted by leap seconds.
• TAI (International Atomic Time) – A continuous atomic time scale, currently 37 seconds ahead of UTC (because of initial offset plus leap seconds). GPS time is actually TAI minus 19 seconds (as of 2024).
• Unix time – Seconds since January 1, 1970, ignoring leap seconds (so it’s similar to GPS time but with a different epoch).
• Julian Date – A continuous day count used in astronomy, often converted to/from GPS time for scientific work.

For most users, the practical difference between GPS and UTC is just the leap-second offset, but for precise applications like navigation, telecommunications, and scientific experiments, the distinction is critical.

Limitations and Accuracy

This converter uses the current leap-second offset (18 seconds as of 2024). If a new leap second is added, the offset changes, and results for dates after that change will be off by one second. The calculator assumes you’re using the standard GPS epoch and week numbering (not the 1,024-week rollover). It also doesn’t account for relativistic effects or satellite clock corrections, which are negligible for everyday conversions but matter for submicrosecond precision. For historical dates before 1980, GPS time is undefined.

Frequently Asked Questions

What is the current GPS week?

As of mid-2024, the GPS week is around 2318 (the exact number changes every Sunday). You can calculate it by taking the number of days since January 6, 1980, dividing by 7, and taking the integer part. Many GPS receivers display the week number, and online tools can show the current value.

Why is GPS time ahead of UTC by 18 seconds?

GPS time started at the same instant as UTC on January 6, 1980, but UTC has had 18 leap seconds added since then (the last one on December 31, 2016). GPS time does not add leap seconds, so it has drifted ahead by that cumulative amount.

How do I convert GPS time to local time?

First convert GPS time to UTC using the leap-second offset, then add your time zone’s offset (e.g., +2 hours for Central European Time). Remember that some regions use daylight saving time, so the offset may change seasonally.

What is GPS week rollover and does it affect me?

GPS week numbers are transmitted as a 10-bit value, so they reset to zero every 1,024 weeks (about 19.7 years). The first rollover was in 1999, the second in 2019. Older receivers may misinterpret the week number after a rollover, but modern devices handle it correctly. When converting manually, add 1,024 (or multiples) to the week number if you’re working with dates after a rollover.

Can I convert a Unix timestamp to GPS time?

Yes. Unix time is seconds since January 1, 1970, ignoring leap seconds. The difference between Unix time and GPS time is constant: GPS time = Unix time − 315,964,800 seconds (the offset between the two epochs, including leap seconds). You can convert Unix to GPS by subtracting that constant, then dividing by 604,800 to get weeks and remainder.

Why do some GPS devices show a different time than my phone?

Your phone typically displays UTC or local time, derived from the GPS signal but corrected for leap seconds and time zone. A raw GPS receiver may show GPS time, which is 18 seconds ahead. Additionally, some devices may not apply the latest leap-second offset, causing a small discrepancy.

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in gps_week | GPS Week | week | 2245 | 0
in gps_seconds | Seconds of Week | s | 345600 | 0
out utc_date | UTC Date/Time | datetime | gps_week*7*86400 + gps_seconds - 18 | 0
out gps_date | GPS Date/Time | datetime | gps_week*7*86400 + gps_seconds | 0