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Maintenance of UTC in the United States is the joint responsibility of the Secretary of Commerce and the Secretary of the Navy. The Secretary of Commerce delegates the timekeeping responsibility to the National Institute of Standards and Technology (NIST, an agency of the Department of Commerce), and the Secretary of the Navy delegates the timekeeping responsibility to the United States Naval Observatory (USNO) in the Department of Defense (DoD). UTC, UTC(NIST) and UTC(USNO) are equivalent at the 20 nanosecond level of accuracy.

How it works

When a user connects to on a computer or mobile device, the Javascript in the client's browser checks the local clock on the device and then requests the time from a NIST server, which has been synchronized with UTC(NIST). When the packets containing the NIST time stamp arrive at the client's browser, the device clock is checked again and compared to the first check of the local clock. The result is a measurement the round-trip delay of requesting/receiving the time stamp. It is estimated that one-half of the round-trip delay happens in each direction. The time on the clocks shown on the web page have been corrected for the estimated one-way path delay of the timestamp from the server to the client and the server delay. Your device's clock is also shown, with the error compared to NIST time.


This website is intended as a time-of-day service only. After receiving the initial timestamp, the time on the running clocks shown is based on the local computer oscillator, so it should not be used to measure frequency or time interval, nor should it be used to establish traceability to NIST or USNO.

Saving Settings - 24 hour clock display

If you would like to make the site default to a 24-hour clock, you can click the box next to  "24 Hour Clock Display" and save a bookmark of the page.  

Improper Use

It is not appropriate to generate your own software to use the functionality of this site, timestamps, server clock, etc.
NO outside applications are permitted to use any of the functionality of this site and this type of use will be blocked.

Setting Your Computer Clock

Many operating systems have time synchronization running periodically, if the device is connected to the Internet. Also, you can download software from NIST, the USNO and other sources in order to use the Internet to automatically set your computer clock to the correct time using the Network Time Protocol (NTP). Mobile phones usually set their clocks periodically according to the time kept at the nearest cellular base station.

Additional Information

For questions about Daylight Saving Time (DST), a.m./p.m., noon/midnight and UTC, check the NIST Time Frequently Asked Questions (FAQ). For time zone offsets around the world, please view a world time zone map. For information about the United Stated Naval Observatory, visit the USNO Precise Time page.


Please send any comments or questions to: timeinfo [at] (subject: (timeinfo[at]nist[dot]gov)
However, due to the volume of email we receive, we cannot always respond to each one individually.

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Created December 23, 2019, Updated October 24, 2023