How to Check the Exact Time

Methods and tools to synchronise with the most accurate time sources available

Why Accuracy Matters

In a world where transactions, communications, and infrastructure all depend on precise timing, knowing the exact time is not a trivial concern. A discrepancy of even one second can cause failures in financial systems, telecommunications networks, and navigation equipment. Whether you need to synchronise a distributed server cluster, verify a timestamp on a legal document, or simply want to set your watch correctly, understanding how to access the most accurate time sources is essential.

Modern civilisation runs on synchronised clocks. The internet, power grids, GPS satellites, and stock markets all rely on time references derived from atomic clocks — the most accurate timekeeping devices ever built. Fortunately, accessing this level of precision is easier than ever, and there are multiple methods available depending on your needs and technical requirements.

450+

Atomic clocks worldwide maintaining UTC

Method 1: Online Time Websites

The simplest way to check the exact time is through a synchronised website. Services like TimePrecise.com display the current time synchronised with atomic clocks via Network Time Protocol (NTP). These sites poll time servers connected to primary atomic clock references and display the result with millisecond accuracy.

When using online time tools, keep in mind that network latency introduces a small delay between the time server and your browser. Most well-designed time websites account for this by using JavaScript to compensate for the measured round-trip time. While you may not achieve nanosecond precision this way, accuracy within a few milliseconds is typical for broadband connections.

Method 2: NIST Internet Time Service

The National Institute of Standards and Technology (NIST) operates the Internet Time Service (ITS), which allows anyone to synchronise their devices with NIST atomic clocks. You can access this service through several protocols:

NTP (Network Time Protocol): The standard protocol for computer clock synchronisation. Configure your operating system to use time.nist.gov or time-a.nist.gov as an NTP server.
HTTP time service: Simply visit time.nist.gov in your browser to see the current NIST time displayed in a simple format.
Automated computer time service (ACTS): A dial-up service for systems without internet access, though this is largely historical now.
Daytime Protocol (port 13): Connect to a NIST server on TCP port 13 to receive a plain-text timestamp.

NIST maintains a ensemble of cesium atomic clocks at its facility in Boulder, Colorado, which contribute to the international calculation of Coordinated Universal Time (UTC). When you synchronise with NIST, you are connecting to one of the most accurate time sources in the world.

Method 3: Operating System NTP Synchronisation

Both Windows and modern Linux and macOS systems come with built-in NTP client support that automatically keeps your computer clock synchronised. By default, most operating systems periodically contact a time server to correct any drift in the local quartz oscillator.

Windows

Windows uses the Windows Time Service (W32Time) to synchronise clocks. By default, it contacts time.windows.com weekly. For better accuracy, you can reconfigure it to use NIST or other stratum-1 NTP servers and increase the synchronisation frequency. Open a command prompt as administrator and run commands to check and modify time synchronisation settings.

Linux and macOS

Unix-like systems typically run an NTP client daemon such as chronyd or ntpd. These services continuously measure and correct clock drift, maintaining accuracy within a few milliseconds. macOS includes a built-in NTP client that synchronises with Apple's time servers by default.

Method 4: GPS Time

The Global Positioning System is powered by atomic clocks aboard each of its 31 satellites. GPS receivers derive extremely accurate time from these satellite signals, typically achieving accuracy within a few nanoseconds. GPS time is maintained by the United States Naval Observatory and is traceable to UTC through a chain of atomic references.

GPS timekeeping is unique because it must account for relativistic effects. Satellites orbit at high velocities (causing time dilation per special relativity) and at high altitudes where gravitational fields are weaker (causing time acceleration per general relativity). Without correcting for these effects, GPS clocks would drift by about 38 microseconds per day, translating to roughly 10 kilometres of positioning error.

While GPS time is extremely accurate, it differs from UTC by a constant offset because GPS time does not implement leap seconds. As of 2026, GPS time is ahead of UTC by 18 seconds. Most GPS receivers convert this offset automatically for consumer display purposes.

Method 5: Radio Time Signals

Radio time signal stations broadcast time information derived from atomic clocks, providing a free and widely accessible method of checking the exact time. Major stations include:

WWVB (United States): Broadcasts from Fort Collins, Colorado on 60 kHz, receivable across most of North America
DCF77 (Germany): Broadcasts on 77.5 kHz, covering most of Europe
MSF (United Kingdom): Broadcasts on 60 kHz from Anthorn, Cumbria
BPC (China): Broadcasts on 68.5 kHz from Shangqiu
JJY (Japan): Broadcasts on 40 kHz and 60 kHz

Radio-controlled clocks and watches contain a small antenna and receiver that automatically decode these signals and set the time with precision typically within one millisecond of UTC. These timepieces are popular for anyone who wants accurate time without manual adjustment.

Method 6: Network Time Protocol (NTP) Deep Dive

NTP is the backbone of time synchronisation across the internet. Developed by David L. Mills in 1985, the protocol uses a hierarchical system of time sources called strata. Stratum 0 refers to the atomic clocks themselves, stratum 1 servers are directly connected to stratum 0 references, stratum 2 servers synchronise with stratum 1 servers, and so on.

NTP achieves accuracy through sophisticated algorithms that measure round-trip network delay, filter out unreliable sources, and compensate for network jitter. A well-configured NTP client on a stable network connection can typically achieve synchronisation within 1 to 10 milliseconds of the reference server. On a local area network with a stratum-1 server, sub-millisecond accuracy is achievable.

Tip: For the best accuracy, configure your system to use multiple NTP servers. NTP's selection algorithms will identify and discard any outliers, providing more reliable synchronisation than any single source alone.

Common Time Sources Compared

Different methods offer different levels of accuracy and convenience. Here is a practical comparison:

Atomic clock (direct): Accuracy to within nanoseconds, but requires expensive equipment costing thousands to millions of dollars
GPS receiver: Accuracy within 10-50 nanoseconds, ideal for field use and portable applications
NTP over broadband internet: Accuracy within 1-10 milliseconds, suitable for most computing needs
Radio-controlled clock: Accuracy within 1 millisecond, good for consumer timekeeping
Smartphone time: Accuracy within 10-100 milliseconds, determined by cell tower synchronisation and NTP
Manual watch setting: Accuracy within seconds if set from an accurate reference, degrades over days

Why Your Devices Drift

Every electronic clock contains an oscillator — a component that produces a regular repeating signal. In consumer devices, this is typically a quartz crystal that vibrates at 32,768 Hz. While quartz is cheap and small, it is affected by temperature changes, aging, electrical noise, and mechanical vibration. These factors cause the frequency to shift slightly, resulting in clock drift of anywhere from a few seconds to over a minute per day.

Temperature is the primary culprit. A quartz crystal rated at 32,768 Hz may oscillate at a slightly different rate when the device heats up during heavy use or cools down in a cold environment. This is why checking and correcting your clock periodically — or relying on automatic synchronisation — is important for maintaining accuracy.

Best Practices for Accurate Time

To ensure you always have access to the exact time, consider these recommendations:

Enable automatic NTP synchronisation on all your computers and devices
Use multiple NTP servers for redundancy and improved accuracy
Consider a GPS time source if you need sub-millisecond accuracy for professional applications
Use synchronised time websites as a quick reference for human-readable exact time
Check your timezone settings — the most accurate clock in the world is useless if set to the wrong timezone
Account for leap seconds if your application requires precise UTC compliance

Explore Related Topics

Live Clock with Seconds - See the current time ticking in real time
Atomic Clocks - The science behind the world's most accurate timekeepers
World Clock - Check the time across every timezone on Earth
Epoch Converter - Convert Unix timestamps to human-readable dates

Frequently Asked Questions

How can I check the exact time right now?

You can check the exact time by visiting time synchronisation websites like TimePrecise.com, using the NIST Internet Time Service, checking your device's built-in NTP synchronisation, or using GPS-based time displays. All of these sources derive their time from atomic clocks.

What is NIST time?

NIST time is the official time maintained by the National Institute of Standards and Technology in the United States. NIST operates a network of atomic clocks and provides the NIST Internet Time Service, which allows computers and devices to synchronise with NIST atomic clocks over the internet.

Why does my computer clock drift over time?

Computer clocks use inexpensive quartz crystal oscillators that are affected by temperature changes, aging, and electrical interference. These factors cause the clock to gradually drift, typically gaining or losing several seconds per day. Regular synchronisation with an NTP server corrects this drift.

How accurate is GPS time?

GPS time is derived from atomic clocks aboard satellites and is accurate to within a few nanoseconds of UTC. However, GPS time does not account for leap seconds, so it may differ from UTC by a few seconds. For most practical purposes, GPS time is extremely accurate.