Time & Date Suite

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Time Zone Calculator: Convert Times Across the World

Convert times between different global zones.

Time Zones

All times stay in sync. Edit any card and the others update to the same moment.

GMT-5-5h local
10:00:18 PM Off-hours
GMT0h local
3:00:18 AM Off-hours
GMT+9+9h local
12:00:18 PM Business hours

How Time Zone Conversion Works

One instant in time can be expressed in many local times. Tokyo at 10 PM is New York at 9 AM the same day. This tool keeps all cards tied to a single UTC timestamp so you can plan across borders without mental math.

Core Concepts

One Moment, Many Clocks

Every card shows the same instant. Change Tokyo to 3 PM and New York, London, and the rest update. The calculator converts your edit to UTC, then displays that UTC moment in each zone using IANA rules.

IANA Time Zones

We use identifiers like America/New_York and Europe/London. They encode daylight saving changes, so winter vs summer offsets are correct without you doing anything.

Business Hours & Day/Night

Green = 9 AMโ€“5 PM local. Sun = daytime; moon = nighttime. Quick visual check for "is anyone awake there?" before you hit send on a meeting invite.

Adding and Syncing

Search cities by name, pick one from the list. New cards inherit the current moment. Trash removes a card. At least one must stay.

Time Zone Calculator: World Clock & Meeting Planner

Convert times between cities. Free world clock for remote teams, meeting planners, and anyone asking "what time is it in Tokyo?" Runs in your browser, no sign-up.

The Math Behind Time Zone Conversion

Every local time can be expressed as a UTC (Coordinated Universal Time) timestamp. For a zone with offset OO hours from UTC, the relationship is UTC=Localโˆ’O\text{UTC} = \text{Local} - O: Tokyo with O=+9O = +9 at 10:00 local gives UTC = 10 โˆ’ 9 = 01:00; New York in winter with O=โˆ’5O = -5 at 10:00 local gives UTC = 10 โˆ’ (โˆ’5) = 15:00. This calculator stores one UTC moment and displays it in each card's zone. Edit any card, we recompute UTC from that input, then update the rest.

Why IANA Time Zones Matter

We use IANA identifiers (America/New_York, Europe/London, Asia/Tokyo) instead of fixed offsets like "UTC-5." IANA includes daylight saving rulesโ€”when New York switches from EST to EDT in March, the offset changes automatically. Same for London (GMT vs BST), Sydney, and 400+ other zones. Past and future dates get the right offset for that moment, so conversions stay accurate across seasons and years.

Use Cases: Meetings, Remote Work, Travel

  • Meeting across time zones:
    Add your cities, pick a time that works. The green business-hours highlight shows when people are likely available. The "Xh local" tag tells you how far ahead or behind each place is from you.
  • What time is it inโ€ฆ?
    Classic world-clock question. Add the city, hit Now, and you see the current time there. Day/night icons tell you at a glance if you're about to wake someone up.
  • Future or past planning:
    Use the date picker for any day. Deadlines, launch times, or "when does that webinar start for me?"โ€”all work. DST is handled for the date you choose.

Time Zone Calculator FAQ

? How do I convert time between different cities?

Add each city with the search bar. Pick a time and date on any cardโ€”the others update instantly to show that same moment. The math: UTC=Localzoneโˆ’Offsetzone\text{UTC} = \text{Local}_{\text{zone}} - \text{Offset}_{\text{zone}} (offset in hours from UTC). Every card shares one UTC timestamp; we display it in each zone's local time.

? What does "+5h local" or "-3h local" mean?

That's how many hours ahead or behind each zone is compared to your computer's clock. +5h means when it's noon for you, it's 5 PM there. Handy when you're wondering "what time is it in London?" or planning a call.

? Why are some times shown in green?

Green marks 9 AMโ€“5 PM local timeโ€”typical business hours. Lets you spot when a remote colleague is likely at their desk so you can find overlapping hours for meetings.

? What are the sun and moon icons for?

Sun means daytime (6 AMโ€“6 PM) in that zone; moon means nighttime. Helps you avoid scheduling a call when it's 2 AM for the other person.

? Does this calculator handle daylight saving time?

Yes. We use IANA time zone IDs (e.g. America/New_York, Europe/London), which include DST rules. Offsets switch automaticallyโ€”EST to EDT, GMT to BSTโ€”so you don't have to guess.
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Time & Date Reference Note

Informational Use: These tools use standard date/time algorithms and your browserโ€™s timezone data (IANA). Results are intended for general reference and planning only.

Verification Recommended: Time zone rules and daylight saving changes vary by region and year. For critical scheduling, payroll, or legal deadlines, confirm results with official sources.

Local Verification: Always confirm times, dates, and business-day counts with official sources or qualified professionals when stakes are high.

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