World Clock & Time Zone Converter

How to use

In World Clock mode, the current time in 8 cities (Tokyo, London, New York, Los Angeles, Paris, Sydney, Dubai, Singapore) updates every second. Use "Add city" to display up to 16 cities. Tokyo is always shown as the reference base and cannot be removed.

In Time Zone Converter mode, select a base city, date, and time. The tool instantly shows what time it will be in each destination city. A "Next Day" or "Previous Day" badge appears when the date crosses midnight. Perfect for scheduling international meetings, planning travel, or coordinating with overseas collaborators.

How it works

Daylight Saving Time (DST) and the Intl API: A common misconception is that the time difference between New York and London is always 5 hours. In reality, it varies by season — from 4 to 6 hours — because the two regions switch to and from daylight saving time on different dates. In 2026, the US starts DST on March 8 while the UK starts on March 29, creating a 3-week window with an unusual offset. Maintaining a manual offset table would require annual updates, but this tool uses the browser's Intl.DateTimeFormat API, which references the OS-level IANA Time Zone Database and handles DST transitions automatically.

UTC, GMT, and IANA time zones: GMT (Greenwich Mean Time) was established at the 1884 International Meridian Conference as an astronomy-based standard. UTC (Coordinated Universal Time) replaced it in 1972, using atomic clocks as the reference. The two differ by at most 0.9 seconds, making them interchangeable for everyday use — but the distinction matters in precision computing and network protocols. There is also an important difference between a UTC offset (+9:00) and an IANA time zone identifier (Asia/Tokyo). A UTC offset is just a number representing the current difference from UTC; an IANA identifier encodes the full history of DST changes and political revisions for that region. This tool uses IANA identifiers rather than hard-coded offsets so that it stays accurate without any maintenance.

Times shown are based on your device's clock. If your device's time is inaccurate, results will reflect that.

Frequently asked questions

How does daylight saving time affect the time difference?

Countries that observe DST shift their clocks forward by 1 hour in spring and back in autumn, so the time difference between two cities can change by 1–2 hours depending on the season. For example, the gap between Tokyo and New York is 14 hours in winter (EST) and 13 hours in summer (EDT). This tool handles all DST transitions automatically via the browser's Intl API — no manual adjustment needed.

What's the difference between UTC and GMT?

GMT (Greenwich Mean Time) is an astronomy-based time standard established in 1884, tied to Earth's rotation. UTC (Coordinated Universal Time) is the modern international standard introduced in 1972, based on atomic clocks. They differ by at most 0.9 seconds and are treated as equivalent in everyday use. This tool uses the "UTC+0" notation, which follows the standard ITU recommendation.

Why does India show a half-hour offset like −3.5 hours?

India Standard Time (IST) is UTC+5:30 — a 30-minute offset rather than a whole hour. This is a historical result of India choosing a single time zone for the entire country and settling on a half-hour increment to balance its geography. Nepal (UTC+5:45) and Iran (UTC+3:30) also use non-integer offsets. This tool displays fractional offsets to one decimal place for accuracy.

Does daylight saving time switch automatically?

Yes, completely automatically. This tool uses the JavaScript Intl.DateTimeFormat API, which reads the IANA Time Zone Database maintained by your operating system. The database contains DST start and end dates for every country, and your OS keeps it up to date. You never need to manually toggle anything.

When should I use this tool versus the date calculator or day-of-week tool?

Use this tool when you need to know what time it is in another city right now, or when a specific date/time in one city corresponds to in another. For counting days between two dates, use the Date Calculator. To find out what day of the week a date falls on, use the Day of Week tool.Date CalculatorDay of Week Calculator

Related Tools

• →Date Calculator
• →Day of Week Calculator
• →Time Calculator