World Clock Time Converter
Instantly convert any time from one city to another, factoring in UTC offsets and daylight saving time. Use it when booking international flights, scheduling calls, or watching live global events.
Last updated: September 2026
Formula below · 2 sources (iana.org, Wikipedia) · Updated Sep 2026
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About this calculator
Time zone conversion works by calculating the net offset between the source and target zones and adding it to the source time: target_time = ((source_hour + source_minute / 60 + (target_offset − source_offset)) mod 24 + 24) mod 24, shown as HH:MM. Each zone's offset depends on the season. In northern summer (roughly mid-March to early November in the US, late March to late October in Europe) Los Angeles, New York, London and Paris are one hour further ahead (UTC−7, UTC−4, UTC+1 and UTC+2), Tokyo never changes (UTC+9), and Sydney is on standard time (UTC+10). In northern winter the US and Europe are on standard time and Sydney is on daylight time (UTC+11). Pick the season that matches your date; for the few weeks when the US, Europe and Australia have changed clocks on different dates, check the exact offsets. The two mod-24 operations keep the result in the 0–24 range whether the raw sum is negative or exceeds 24.
How to use
Convert 08:45 New York to London in summer (northern summer selected). Step 1 — source decimal: 8 + 45/60 = 8.75. Step 2 — summer offsets: New York is on EDT (UTC−4) and London on BST (UTC+1), a difference of +5. Step 3 — raw sum: 8.75 + 5 = 13.75. Step 4 — apply mod 24: 13.75, shown as 13:45 London time. So an 8:45 AM New York meeting is 1:45 PM in London in summer (and also in winter, when both are on standard time). New York to Sydney differs by season: 08:45 New York is 22:45 Sydney in northern summer (UTC−4 → UTC+10) but 00:45 the next day in northern winter (UTC−5 → UTC+11).
Frequently asked questions
How does daylight saving time affect world clock conversions?
Daylight saving time (DST) shifts clocks forward by one hour in participating regions during their summer. In this calculator, choose the season: in northern summer the US and European zones each add 1 hour to their offset while Tokyo stays at UTC+9 and Sydney is on standard time (UTC+10); in northern winter the US and Europe are on standard time and Sydney adds 1 hour (UTC+11). Because the US, Europe and Australia change clocks on different dates, verify the offsets for a date within a few weeks of a change.
What does a negative UTC offset mean in time zone conversion?
A negative UTC offset means the location is west of the prime meridian and behind UTC. For example, UTC−5 (Eastern Standard Time) is 5 hours behind London. When you subtract a negative offset — e.g., target (UTC+1) minus source (UTC−5) — you get +6, meaning the target location is 6 hours ahead. The calculator handles this automatically through signed arithmetic, so you just enter the correct offset with its sign.
Why does the calculator use two mod-24 operations instead of one?
A single mod 24 can return a negative number in JavaScript when the input is negative (e.g., −2 mod 24 = −2 in some engines). Adding 24 before the second mod ensures the result is always non-negative: (x mod 24 + 24) mod 24 maps any value — however negative — into the 0 to 23.99 range. This double-modulo pattern is a defensive programming convention for clock arithmetic.