ZeroKit

Loading tool…

How to Convert Time Between Time Zones

Time zone conversion adds or subtracts the UTC-offset difference between two locations. Daylight Saving Time can shift the offset seasonally.

  1. Identify the UTC offset of both the source and target time zones. For example, New York (EST) is UTC−5, London (GMT) is UTC+0.
  2. Calculate the difference: Target offset − Source offset. London − New York = 0 − (−5) = +5 hours.
  3. Add the difference to the source time: 10:00 AM in New York + 5 hours = 3:00 PM in London.
  4. Check for date changes: if adding hours crosses midnight, move the date forward (or backward for negative differences).
  5. Account for Daylight Saving Time. During summer, New York switches to EDT (UTC−4), reducing the gap to 4 hours when London is on GMT, or 5 hours when London is on BST (UTC+1). Always verify the DST schedule for both locations.

Timezone Conversion Formula

Target Time = Source Time + (Target UTC Offset − Source UTC Offset). UTC offsets range from −12 to +14 hours. Some zones use 30- or 45-minute offsets (e.g. India at UTC+5:30, Nepal at UTC+5:45). Daylight Saving Time shifts the offset by one hour (occasionally 30 minutes) for part of the year. This calculator uses the browser's Intl API, which applies the IANA time-zone database — the same authoritative source used by operating systems worldwide.

Why Use Our Timezone Converter?

  • Powered by the IANA database — the same data your operating system uses, accessed via the Intl API.
  • Business-hours indicator — instantly see whether the target city is inside 9 AM–5 PM working hours.
  • World clock panel — view current time in 10 major cities at a glance.
  • DST-aware — Daylight Saving shifts are handled automatically for every zone.
  • Completely private — no server call, no location tracking, no cookies.

Frequently Asked Questions

What is UTC?

UTC (Coordinated Universal Time) is the global time standard from which all time zones are measured as positive or negative offsets. It replaced GMT as the reference standard in 1960 and does not observe Daylight Saving Time.

What is the difference between GMT and UTC?

For most practical purposes they are identical — both refer to the time at the prime meridian (0° longitude). Technically, GMT is a time zone used by some countries, while UTC is the scientific time standard maintained by atomic clocks. UTC does not change with DST; GMT the time zone does not either, but the UK switches to BST (UTC+1) in summer.

How does Daylight Saving Time affect the conversion?

DST shifts a time zone's offset by one hour (or occasionally 30 minutes). Because not all countries observe DST — and those that do may switch on different dates — the UTC difference between two cities can change throughout the year. This tool uses the IANA database, which tracks every DST rule worldwide.

Why do some time zones have 30- or 45-minute offsets?

Historical and political reasons. India (UTC+5:30), Iran (UTC+3:30), Nepal (UTC+5:45), and parts of Australia (UTC+9:30) adopted non-whole-hour offsets to better align solar noon with clock noon, or to differentiate themselves from neighbouring countries.

How do I plan a meeting across multiple time zones?

Use the world-clock panel to see the current time in all relevant cities at once. Look for a window where all locations are within business hours (9 AM–5 PM). The green/red dot next to each city indicates whether it is currently in business hours.

Is my location tracked?

No. The tool detects your device's configured time zone via the browser API (Intl.DateTimeFormat) but does not use GPS, IP geolocation, or any server-side lookup. No location data is stored or transmitted.