GPS Time Calculator
Convert between UTC date/time and GPS week + seconds of week. This is useful for GNSS logs, telemetry, navigation testing, and satellite data analysis.
UTC to GPS
GPS to UTC
What is GPS time?
GPS time is the internal timescale used by Global Positioning System satellites. It started at midnight on January 6, 1980, and it does not insert leap seconds. By contrast, UTC (Coordinated Universal Time) does insert leap seconds to stay aligned with Earth rotation. Because of that design choice, GPS and UTC gradually diverge.
In practice, engineers often represent GPS time as:
- GPS Week (number of weeks since GPS epoch)
- Seconds of Week (SOW) (seconds elapsed within the current week)
How this GPS time calculator works
UTC to GPS conversion
To convert UTC to GPS, the calculator computes the elapsed seconds from the GPS epoch and then adds the current GPS-UTC offset. With today’s commonly used offset (18 seconds), GPS time is ahead of UTC.
- Step 1: Convert UTC date/time into a timestamp
- Step 2: Subtract GPS epoch (1980-01-06 00:00:00)
- Step 3: Add GPS-UTC offset
- Step 4: Split into week number and seconds of week
GPS to UTC conversion
For reverse conversion, the calculator combines week and SOW into total GPS seconds since epoch, subtracts the GPS-UTC offset, and returns a UTC timestamp and Unix time.
Why the GPS-UTC offset matters
If a leap second is introduced in the future, the offset will change. That means a fixed conversion can become wrong if your software assumes an old value forever. This tool exposes the offset input so you can update it without rewriting code.
Tip: for archived datasets, use the offset that was valid at the time of measurement.
Common use cases
- Decoding GNSS receiver logs that store GPS week and SOW
- Synchronizing sensor payloads to UTC timelines
- Converting navigation test vectors between simulation and field data
- Validating timestamps in robotics, drones, and autonomous systems
- Troubleshooting timing drift across distributed systems
Practical notes for developers
1) Week rollover awareness
Some devices transmit reduced week counters (for example, 10-bit week values). If your source data uses a truncated week value, you may need additional context (date bounds, firmware assumptions, mission timeline) to map it to the correct full week.
2) Time zone confusion
GPS conversions should be done in UTC, not local time. This page treats the selected date/time as UTC for consistent conversion. If you enter local wall-clock time by mistake, the output will be shifted by your local UTC offset.
3) Sub-second precision
This calculator supports fractional seconds in SOW input. For high-precision applications, confirm your receiver’s clock model, oscillator quality, and any transport delay corrections.
Quick FAQ
Is GPS time the same as Unix time?
No. Unix time starts in 1970 and tracks UTC seconds, while GPS time starts in 1980 and does not include leap seconds.
Is GPS time ahead of UTC?
Yes. With an offset of 18 seconds, GPS is 18 seconds ahead of UTC.
Can I use this as a GPS week calculator?
Absolutely. Enter a UTC timestamp and the tool returns the GPS week and seconds of week directly.
Bottom line
If you work with navigation, telemetry, or satellite data, a reliable UTC to GPS time converter is essential. Use the calculator above to move between UTC and GPS week/SOW quickly, while keeping leap-second behavior explicit and controllable.