About Clock.now
What is Clock.now?
Clock.now is a precise, server-synced time service that shows you the exact current time for any city, country, or time zone in the world. Unlike your device clock - Which may drift by seconds or minutes - Clock.now syncs with our server every time you load a page and calculates the offset between your device and our server.
How does the clock sync work?
When you visit Clock.now, our JavaScript immediately fetches the current server time from /api/time/now. It then calculates the difference between the server's time and your device's clock. Every second thereafter, the displayed time is corrected by this offset - So even if your device clock is 30 seconds wrong, Clock.now shows the accurate time.
Time Zone Data
All time zone data is sourced from the IANA Time Zone Database (also known as the Olson database or tzdata). This is the authoritative source used by operating systems, programming languages, and internet standards worldwide. We use Python's zoneinfo module backed by the tzdata package.
Features
- ✓ Live clock synced with server time
- ✓ Current time for 200+ countries and thousands of cities
- ✓ Time zone converter
- ✓ Meeting planner — find overlap hours across global teams
- ✓ World clock with interactive map
- ✓ Hours from now, minutes from now, days from now, and more
- ✓ Unix timestamp converter
- ✓ Countdown timer and interval timer with alert
- ✓ Stopwatch with lap times
- ✓ Date calculator — days between any two dates
- ✓ Age calculator — years, days, hours, heartbeats since birth
- ✓ Historical events — 395+ events with exact day counts
- ✓ Save favourite locations (free account)
- ✓ Email reminders for specific times
How Clock.now Works
Server Sync via API
The moment any page loads, the browser sends a request to /api/time/now. The server responds with the precise UTC timestamp sourced from the system clock, which is kept accurate by the host's NTP (Network Time Protocol) daemon. This handshake takes milliseconds and establishes the ground truth for every clock on the page.
Offset Calculation
Once the server timestamp arrives, the browser compares it against Date.now() - The device's own clock reading at that instant. The difference between the two values is stored as a signed offset in milliseconds. A positive offset means the device clock runs ahead of the server; a negative offset means it runs behind. This offset is calculated once per page load.
Per-Second Correction
Every second, a setInterval tick fires. Instead of displaying the raw device time, Clock.now adds the stored offset to the current Date.now() value before formatting it. This means even if your laptop's clock has drifted by 45 seconds, every city clock on the site remains correct to within the round-trip latency of the initial API call - Typically under one second.
Our Data Sources
IANA Time Zone Database (tzdata)
Every offset, DST rule, and historical transition shown on Clock.now comes from the IANA Time Zone Database - The definitive, open-source record of how every political jurisdiction has defined local time since timekeeping was standardized. Maintained by a team of volunteer editors since 1986, the database is updated multiple times per year as governments announce changes. Python's zoneinfo module reads this data directly, ensuring Clock.now is always current within one package update cycle.
NTP - Network Time Protocol
The server that powers Clock.now synchronizes its system clock with a pool of atomic-clock-backed NTP servers. NTP is the internet's universal time-keeping protocol, operating since 1985. It works by measuring the round-trip delay between client and server, then correcting for that delay to set the local clock to within a few milliseconds of UTC. Our server typically maintains accuracy within 10 ms of true UTC at all times.
DST Transition Tracking
Daylight Saving Time rules are encoded directly in the IANA database as POSIX-style transition rules. Clock.now evaluates these rules at query time so that a time zone that transitions at 2:00 AM on a specific Sunday in March is handled correctly - Including the ambiguous "fall-back" hour and the skipped "spring-forward" hour. Cities that do not observe DST (Japan, India, China, and most of Africa, for example) are flagged accordingly and their offsets never change.
Frequently Asked Questions
What makes Clock.now accurate? +
How do I convert time zones on Clock.now? +
Is the time shown in UTC or local time? +
How is Daylight Saving Time handled? +
Can I embed a Clock.now clock on my site? +
/api/time/now endpoint returns a JSON object with the current UTC timestamp, server offset, and ISO-formatted date string.