How are the time zone offsets calculated - is daylight saving handled?

Yes. Every offset is computed with the browser's built-in Intl.DateTimeFormat against the IANA time zone database, using the exact base instant you choose. That means daylight saving transitions are applied automatically: a US zone shows -5 hours (EST) in January and -4 hours (EDT) in July, and the change happens at the correct boundary. There are no hardcoded offset tables in this tool, so the data cannot drift out of date the way a static lookup would.

What do the +1 day and -1 day badges mean?

They show that a zone is on a different calendar day than your base zone for the selected instant. For example, when it is late evening in New York it can already be the next morning in Tokyo, so Tokyo gets a +1 day badge. The relative label (such as "+14h, tomorrow") gives the same information in words. This makes it obvious when scheduling that a colleague is effectively in your past or future day.

How does the meeting planner decide on overlapping hours?

It takes the 24 hours of the base zone's current day and, for each hour, computes the local hour in every selected zone. An hour is working hours for a zone when its local time is between 09:00 and 17:00. A column turns solid green only when that hour is inside working hours for every zone at once, so the solid-green columns are your candidate meeting slots. If nothing is solid green, there is no 9-to-5 overlap and someone will need to take the call early or late.

Which export formats are available and when should I use each?

Four targets. Intl.DateTimeFormat is dependency-free and runs anywhere modern JavaScript runs - the default choice. date-fns-tz (formatInTimeZone) suits projects already using date-fns. Luxon (DateTime.fromMillis().setZone()) is ideal if you prefer Luxon's immutable DateTime API. The plain ISO list is a non-code, copy-paste summary of each zone's date, time, and offset for pasting into a ticket, doc, or chat message.

Can I share or bookmark a specific set of zones and time?

Yes. The full configuration - your selected zones and their order, the base zone, the base instant, the 24-hour toggle, and the export format - is encoded into the page URL. Copy the share link (or just bookmark the page) and anyone who opens it sees the exact same world clock and planner state, frozen to the instant you shared rather than snapping to their current time.

Does it support every time zone or just a popular subset?

It supports the complete IANA time zone list reported by your browser via Intl.supportedValuesOf - typically 400+ zones. The quick-add chips and the base-zone helpers surface a curated set of common business zones, but the "Add a zone" search lets you reach any IANA identifier, from Pacific/Chatham to Asia/Kathmandu, including the half-hour and 45-minute offsets.

Time Zone Converter

A live world clock and meeting planner. Add any IANA time zones, scrub a base instant with the hour slider, and watch every zone update with DST-correct offsets and next-day badges. Find the working-hours overlap across teams, then export the conversion as Intl, date-fns-tz, Luxon, or a plain ISO list.

About this ToolHow it works, benefits & use cases

Most time zone tools convert one time between two zones and stop there. This one is a live world clock and meeting planner built on the browser's own Intl API and the full IANA time zone database. Add any number of zones, pick a base zone, then set a base instant with the date-time picker or scrub the hour slider and watch every zone update at once - with the correct UTC offset, the local date, a +1 day / -1 day badge when a zone has crossed the date line, and a DST indicator when a zone is on summer time. Because the offsets come straight from Intl.DateTimeFormat, daylight saving transitions are handled automatically and correctly, with no hardcoded offset tables to go stale. The meeting planner lays the 24 hours of the base day across every zone and highlights the hours that fall inside 9-to-5 working hours for all of them, so you can find a slot that works for a distributed team at a glance. When you have the configuration you want, export it as ready-to-paste code for Intl.DateTimeFormat, date-fns-tz, or Luxon, or as a plain ISO list - and the entire setup lives in a shareable URL.

How to Use

1Quick-add common zones from the chips, or search the full IANA list in the "Add a zone" dropdown.
2Click any zone in the world clock to make it the base zone - day deltas and the planner are computed relative to it.
3Set the moment with the date-time picker, press "Now" for the current instant, or drag the hour slider to scrub through the day.
4Read the meeting planner strip: solid green columns are hours inside working hours (9-17) for every selected zone.
5Pick an output format (Intl, date-fns-tz, Luxon, or ISO list) and copy the snippet, or share the URL to reproduce the exact view.

Key Benefits

DST-correct offsets straight from Intl and the IANA database - no manual offset tables to maintain
Live world clock with local time, date, UTC offset, relative label, and a DST indicator per zone
+1 day / -1 day badges make date-line crossings impossible to miss
Meeting planner highlights the working-hours overlap across every selected zone at once
Scrub the hour slider to preview how a meeting time lands in every zone instantly
Export to Intl.DateTimeFormat, date-fns-tz, Luxon, or a plain ISO list
Reorderable, removable zones and a fully shareable URL of the whole setup

Common Use Cases

Scheduling a standup or call across a distributed team in several countries
Checking what time a deploy window or maintenance start lands for users worldwide
Generating the exact Intl, date-fns-tz, or Luxon code to format a timestamp per zone
Sanity-checking how a date-line crossing shifts the calendar day for a far-east colleague
Confirming whether a US, EU, or Australian zone is currently observing daylight saving time

World clock

base: Eastern Time (US & Canada)

04:00
Jan 15, 2025
07:00
Jan 15, 2025
12:00
Jan 15, 2025
21:00
Jan 15, 2025

Meeting planner

no shared working hours

Pacific Time (US & Canada)

Eastern Time (US & Canada)

London (GMT/BST)

Japan Standard Time

Each column is one hour of the base zone's day (0–23h). Solid green = inside working hours for every zone.

Base time

Base zone

Date & time (in base zone)

Scrub hour07:00 base

24-hour clock

Zones

Add a zone

Quick add

Export

Output format

Conversion snippet

Base instant: 2025-01-15T12:00:00.000Z

const instant = new Date("2025-01-15T12:00:00.000Z");

const times = {
  "America/Los_Angeles": new Intl.DateTimeFormat('en-US', { timeZone: "America/Los_Angeles", dateStyle: 'medium', timeStyle: 'short', hour12: false }).format(instant),
  "America/New_York": new Intl.DateTimeFormat('en-US', { timeZone: "America/New_York", dateStyle: 'medium', timeStyle: 'short', hour12: false }).format(instant),
  "Europe/London": new Intl.DateTimeFormat('en-US', { timeZone: "Europe/London", dateStyle: 'medium', timeStyle: 'short', hour12: false }).format(instant),
  "Asia/Tokyo": new Intl.DateTimeFormat('en-US', { timeZone: "Asia/Tokyo", dateStyle: 'medium', timeStyle: 'short', hour12: false }).format(instant),
};

console.log(times);

DST-correct by construction

Every offset here comes from the browser's built-in Intl.DateTimeFormat with the IANA database, so daylight saving transitions are handled automatically. Scrub the base hour and you will see a US zone jump from EST to EDT at the right boundary, while a no-DST zone like Tokyo stays put. No library, no hardcoded offset table.

Plan across the date line

The +1 day / -1 daybadges and the relative labels ("+9h, tomorrow") make it obvious when a colleague is already in the next calendar day. The meeting planner then highlights the hours that land inside 9–17 working hours for every selected zone at once.

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Time Zone Converter

How to Use

Key Benefits

Common Use Cases

World clock

Meeting planner

Base time

Zones

Export

DST-correct by construction

Plan across the date line

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Frequently Asked Questions - Timezone Converter