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Share sensitive information only on official, secure websites. https://www.nist.gov/pml/time-and-frequency-division/time-services/ ut1-ntp-time-dissemination National Institute of Standards and Technology National Institute of Standards and Technology Search NIST [ ] Search Menu Close * Topics + All Topics + Advanced communications + Artificial intelligence + Bioscience + Buildings and construction + Chemistry + Climate + Cybersecurity + Electronics + Energy + Environment + Fire + Forensic science + Health + Information technology + Infrastructure + Manufacturing + Materials + Mathematics and statistics + Metrology + Nanotechnology + Neutron research + Performance excellence + Physics + Public safety + Resilience + Standards + Transportation * Publications * Labs & Major Programs + Laboratories o Communications Technology Laboratory o Engineering Laboratory o Information Technology Laboratory o Material Measurement Laboratory o Physical Measurement Laboratory + User Facilities o NIST Center for Neutron Research o CNST NanoFab + Research Test Beds + Research Projects + Tools & Instruments + Major Programs o Baldrige Performance Excellence Program o Manufacturing Extension Partnership (MEP) o Office of Advanced Manufacturing o Special Programs Office o Technology Partnerships Office * Services & Resources + Standards and Measurements o Calibration Services o Laboratory Accreditation (NVLAP) o Quality System o Standard Reference Materials (SRMs) o Standards.gov o Time Services o Office of Weights and Measures + Software + Data o Chemistry WebBook o National Vulnerability Database o Physical Reference Data o Standard Reference Data (SRD) + Storefront + License & Patents + Computer Security Resource Center (CSRC) + NIST Research Library * News & Events + News + Events + Blogs + Feature Stories + Awards + Video Gallery + Image Gallery + Media Contacts * About NIST + About Us + Contact Us + Visit + Careers + Our Organization o Office of the Director o Budget & Planning + Industry Impacts + Work with NIST + History o NIST Digital Archives o NIST Museum o NIST and the Nobel + Resources for Kids Physical Measurement Laboratory / Time and Frequency Division Time Realization and Distribution * Laboratory Homepage * Division Homepage * Official United States Time * Groups Expand or Collapse + Atomic Devices and Instrumentation + Ion Storage + Optical Frequency Measurements + Time Realization and Distribution + Time and Frequency Metrology * Popular Links Expand or Collapse + A Walk Through Time + Daylight Saving Time (DST) + Help with Radio Controlled Clocks + Telephone Time-of-Day Service (TTDS) + Time & Frequency from A - Z + Web Clock FAQ * Publications * Staff Directory * Time Distribution Expand or Collapse + Automated Computer Time Service (ACTS) + GPS Data Archive + GPS Time Transfer + Internet Time Service (ITS) + Radio Station WWV + Radio Station WWVB + Radio Station WWVH + Remote Frequency Calibrations (FMAS) + Remote Time Calibrations (TMAS) + Telephone Time-of-Day (TTDS) + Two-Way Satellite Time and Frequency Transfer (TWSTFT) * Time Realization Expand or Collapse + Leap Seconds + Primary Standard (NIST-F1) + Time Scale Data and Bulletin Archive + UTC(NIST) Time Scale UT1 NTP Time Dissemination Share Facebook Linkedin Twitter Email The Time and Frequency Division of NIST offers a network time service to deliver UT1 time. The service will be implemented by time servers which transmit UT1 time in standard NTP format. (For example, see RFC 1305 for an explanation of the NTP format.) These servers should respond to time requests in NTP versions 3 or 4 from most standard NTP clients. The servers will treat all requests in client-server mode independent of the actual mode of the request. Broadcast modes are not supported. The reply will have no special indication that the transmitted time is UT1 and not UTC. The servers will be synchronized to UTC(NIST) with an offset of approximately 1 microsecond RMS. The difference between UTC(NIST) and UTC is typically a few nanoseconds, and is tabulated in Circular T of the BIPM, which is published monthly. (www.bipm.org ). Rapid UTC (UTCr) gives daily values of the difference between UTC and UTC(NIST) and is computed by the BIPM at more frequent intervals. The servers will compute UT1 time by adding the DUT1 value for any MJD to UTC(NIST). The value used for DUT1 will be the value determined by the IERS (http://www.iers.org) and published in IERS Schedule A for the MJD of the request when it is received by the servers and with a single linear interpolation between consecutive MJD values. The accuracy of a time message received by a user will be limited by the stability and reciprocity of the network delay between the user's system and the servers. It will generally be no better than a few milliseconds, but may be much poorer and might be better than this value in some particularly favorable circumstances. This system supports open access and no registration is required. Here are the server names, locations, and IP addresses for NIST Internet Time Service - the UT1 servers are at the bottom of the page. Send comments or questions: Time and Frequency Division NIST Mail Stop 847 325 Broadway Boulder, Colorado 80305 judah.Levine [at] nist.gov Time and frequency Contacts * Judah Levine judah.levine@nist.gov (303) 497-3903 Created December 11, 2015, Updated June 2, 2021 National Institute of Standards and Technology logo HEADQUARTERS 100 Bureau Drive Gaithersburg, MD 20899 301-975-2000 Webmaster | Contact Us | Our Other Offices Twitter Facebook LinkedIn Instagram YouTube RSS Feed Mailing List How are we doing? Feedback * Site Privacy * Accessibility * Privacy Program * Copyrights * Vulnerability Disclosure * No Fear Act Policy * FOIA * Environmental Policy * Scientific Integrity * Information Quality Standards * Commerce.gov * Science.gov * USA.gov * Vote.gov