Java Programs›Date & Time›Convert Time Between Time Zones

Convert Time Between Time Zones in Java

intermediate· Date & Time · Date & Time

Problem

A ZonedDateTime pairs a date-time with a region's time-zone rules, so the same instant can be shown as the correct local time anywhere, daylight saving included.

A meeting starts at 09:30 on 9 March 2026 in India; show the local time for attendees in London, New York and Tokyo.

Input

2026-03-09 09:30 Asia/Kolkata

Output

London 04:00, New York 00:00, Tokyo 13:00

Java Program

Java

import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Locale;

public class ConvertTimeZones {
    public static void main(String[] args) {
        ZonedDateTime india = ZonedDateTime.of(LocalDateTime.of(2026, 3, 9, 9, 30), ZoneId.of("Asia/Kolkata"));
        DateTimeFormatter f = DateTimeFormatter.ofPattern("d MMM yyyy HH:mm (xxx)", Locale.ENGLISH);

        String[] zones = {"Asia/Kolkata", "Europe/London", "America/New_York", "Asia/Tokyo"};
        for (String zone : zones) {
            ZonedDateTime local = india.withZoneSameInstant(ZoneId.of(zone)); // same moment, different clock
            System.out.println(String.format("%-17s %s", zone, local.format(f)));
        }
    }
}

▶ Run Code

Output

Asia/Kolkata      9 Mar 2026 09:30 (+05:30)
Europe/London     9 Mar 2026 04:00 (+00:00)
America/New_York  9 Mar 2026 00:00 (-04:00)
Asia/Tokyo        9 Mar 2026 13:00 (+09:00)

Core Logic

withZoneSameInstant keeps the moment fixed and recalculates the wall-clock time for another zone.

How It Works

1ZonedDateTime.of(..., ZoneId.of("Asia/Kolkata")) fixes the meeting in Indian time (UTC+05:30).
2For each target zone, withZoneSameInstant(ZoneId.of(zone)) converts it.
3The xxx pattern letter prints each zone's UTC offset.
4String.format("%-17s ...") pads the zone names into a neat column.

New York shows −04:00, not −05:00, because US daylight saving began on 8 March 2026 — the zone rules handle that automatically.

💡

Key Point: Use region IDs such as America/New_York rather than fixed offsets like -05:00, so daylight-saving changes are applied for you.

Key Concepts

ZonedDateTimeZoneIdwithZoneSameInstant()UTC offset

Approach 2: Starting from a UTC Instant

Java

import java.time.Instant;
import java.time.ZoneId;

public class ConvertTimeZonesInstant {
    public static void main(String[] args) {
        Instant moment = Instant.parse("2026-03-09T04:00:00Z"); // a single point on the UTC timeline

        System.out.println("UTC instant: " + moment);
        System.out.println("In Kolkata:  " + moment.atZone(ZoneId.of("Asia/Kolkata")).toLocalDateTime());
        System.out.println("In New York: " + moment.atZone(ZoneId.of("America/New_York")).toLocalDateTime());
    }
}

▶ Run Code

Output

UTC instant: 2026-03-09T04:00:00Z
In Kolkata:  2026-03-09T09:30
In New York: 2026-03-09T00:00

Core Logic

Servers usually store times as an Instant — a point on the UTC timeline — and convert to a zone only when displaying it.

How It Works

1Instant.parse("2026-03-09T04:00:00Z") reads a UTC timestamp (the Z means UTC).
2atZone(ZoneId.of(...)) attaches a zone, producing a ZonedDateTime.
3toLocalDateTime() drops the zone to show just the local clock reading.

04:00 UTC is 09:30 in Kolkata and midnight in New York — the same moment as the main program.

💡

Key Point: Store instants in UTC and convert at the edges; storing local times without a zone makes them ambiguous later.