GPS Epoch Time Converter: What It Is and How to Use It

A GPS epoch time converter translates between GPS time (the continuous count of weeks and seconds since January 6, 1980) and standard UTC calendar dates. You enter a GPS week and seconds-of-week (or a UTC date/time), and the converter returns the corresponding date/time in the other format, accounting for the 18 leap seconds that currently separate the two scales.

Formula

The core formula is: UTC = GPS epoch + (GPS week × 604,800) + seconds-of-week − leap_seconds

• GPS epoch = January 6, 1980, 00:00:00 UTC
• GPS week = the integer week number since the epoch (no rollover in this converter)
• Seconds of week = 0 to 604,799 (one week = 7 × 24 × 3600 = 604,800 seconds)
• Leap seconds = 18 (as of 2025; see note below)

The result is a UTC date/time. To get local time, add your timezone offset (e.g., +5 for EST, −8 for PST).

Worked Example

Using the defaults in the calculator above: GPS week 2300, seconds of week 345,600 (which is 4 days × 86,400 s/day).

1. Total seconds from GPS epoch = (2300 × 604,800) + 345,600 = 1,391,040,000 + 345,600 = 1,391,385,600 seconds
2. Subtract 18 leap seconds → 1,391,385,582 seconds
3. Add to the epoch: Jan 6, 1980 + 1,391,385,582 seconds = 2024-02-05 00:00:00 UTC

The converter shows the same: 2024-02-05 00:00:00 UTC.

Why GPS Time Differs from UTC

GPS time was set to match UTC on January 6, 1980, but it does not follow leap seconds. UTC periodically adds a leap second to keep civil time aligned with Earth’s rotation. GPS time ignores those additions, so the difference grows over time. As of 2025, the difference is 18 seconds. This is not a drift or error—it’s a deliberate design choice for navigation consistency.

When converting, you must know the current leap second count. The International Earth Rotation and Reference Systems Service (IERS) announces new leap seconds; the last one was added on December 31, 2016. If another is added, the offset changes.

Common Use Cases

• Aviation and marine navigation: GPS receivers output time in GPS time; pilots and sailors often need UTC for logs and coordination.
• Network time synchronization: NTP servers use UTC, but some systems log in GPS time for precision.
• Scientific data logging: Research instruments may timestamp with GPS time; converting to UTC allows comparison with other datasets.
• Software debugging: When analyzing GPS module output, you may need to convert week/seconds to a human-readable timestamp.

How to Use the Converter

1. Enter a GPS week number (e.g., 2300) and seconds of week (0–604,799).
2. The converter instantly shows the corresponding UTC date/time.
3. To convert from UTC to GPS, you can reverse the formula: GPS seconds = (UTC − epoch) + leap_seconds, then divide by 604,800 for weeks.

For a date like 2024-02-05 00:00:00 UTC, the GPS week is 2300 and seconds of week is 345,600 (since that’s 4 days into the week).

Common Mistakes and Pitfalls

• Forgetting leap seconds: Using 0 instead of 18 gives a time 18 seconds late—small but critical for precise applications.
• Week rollover: GPS week numbers roll over every 1024 weeks (about 19.7 years). The most recent rollover was April 6, 2019. Some older receivers reset to week 0, causing errors.
• Seconds of week range: Values must be between 0 and 604,799. Values ≥604,800 spill into the next week.
• Mixing up UTC and local time: The converter outputs UTC; you must add your timezone offset manually.

GPS Week Rollover

GPS week numbers are transmitted as a 10-bit field, so they wrap from 1023 to 0. The first rollover occurred in August 1999, the second in April 2019. Modern receivers handle this automatically, but older devices may need a firmware update. When converting historical data, ensure you know which epoch the week number refers to (the original or the rollover-adjusted).

Alternatives and Related Time Scales

• Unix time: Seconds since January 1, 1970, UTC. It also ignores leap seconds (mostly), so the difference from GPS time is 18 + 10 = 28 seconds (as of 2025).
• TAI (International Atomic Time): A continuous time scale with no leap seconds. GPS time is TAI minus 19 seconds (constant offset).
• UTC: The civil time standard that includes leap seconds.

If you work with multiple systems, always verify which time base you’re using.

Frequently Asked Questions

What is the current GPS-UTC offset?

As of 2025, the offset is 18 seconds. This means GPS time is ahead of UTC by 18 seconds. The offset changes only when a new leap second is added to UTC.

Why does my GPS receiver show a different time than my phone?

Your phone typically displays UTC or local time, not raw GPS time. The GPS receiver internally uses GPS time, but the operating system converts it to UTC for display. If you see a discrepancy, it’s likely due to the leap second offset or a timezone setting.

How do I convert GPS time to Unix time?

Unix time is seconds since 1970-01-01. The difference between GPS and Unix time is 28 seconds (as of 2025): GPS time = Unix time + 28. So to convert GPS to Unix, subtract 28 from the GPS seconds (after converting to a common epoch).

Does the converter handle GPS week rollover?

No, it assumes a linear week number without rollover. If you have a week number from a device that rolled over, add 1024 to it for each rollover since 1980. For example, week 5 after the 2019 rollover is actually week 1029 in the linear scale.

Can I convert a UTC date to GPS week and seconds?

Yes, reverse the formula: compute the total seconds from the GPS epoch to your UTC date, add 18 leap seconds, then divide by 604,800 to get weeks and the remainder to get seconds of week.

Related

• Buffer Formulation Calculator: How to Mix
• Variation Formula: How to Calculate It
• XRD Peak Shift to Lower Angle: Causes & Meaning

in gps_week | GPS Week | - | 2300 | 0
in gps_sec | Seconds of Week | s | 345600 | 0
out utc_date | UTC Date/Time | - | datetime(1980,1,6) + (gps_week * 604800 + gps_sec - 18) | 0