Hours apart
Time Zone Difference
Offset between two cities on a chosen date, including DST.
Time zone difference
Pick two cities and a date.
Time zone difference answers one numeric question: how many hours apart two IANA cities are on a date you pick, after daylight-saving rules for that date are applied. You choose city A, city B, and a civil date. The result states which city is ahead, by how much, and the UTC offset of each side. It does not find a shared work hour and it does not convert a meeting’s wall clock into another city. Those jobs need other pages.
Hours apart on one civil date
The gap is the difference between two offsets at one shared instant. This page uses 12:00 UTC on the chosen date so both cities are evaluated on the same absolute moment. That avoids asking which city’s noon to prefer. The printed sentence names city A relative to city B: ahead, behind, or the same offset. Swap the two pickers if you want the sentence written the other way; the absolute gap is unchanged.
Offsets come from the IANA database via the browser. New York versus London is often five hours in winter and four in summer, because the two regions do not switch DST on the same weekend. A remembered “always five hours” rule fails in March and October. Recalculate for the actual travel or call date rather than reusing last July’s figure.
If you only need to see what time it is in many places right now, the world clock is the matching tool. If you need this device’s own IANA name, use the timezone detector instead of inventing a city that happens to share your offset.
Why the date field exists
DST transitions are the reason a date is required. The United States currently springs forward in March and falls back in November. The European Union uses late March and late October. Australia’s states that observe DST do so in the opposite half of the year. A pair can therefore show three different gaps in a single twelve-month span: both on standard time, both on daylight time, or only one side switched.
Pick the date of the flight, the broadcast, or the contract milestone. Using “today” for a November call while you sit in May will misstate the gap if one side will have changed clocks by then. Historical dates also matter for log review: an outage timestamp from last spring should be decoded with that spring’s rules, not with this week’s offsets.
The date is a calendar day in UTC for the comparison instant. Near the Date Line the two cities may already be on different local dates at 12:00 UTC. The gap is still a valid offset difference; it is not a claim that both wall calendars show the same weekday. Pair the number with local clocks if you need the weekday in each city.
Half hours and forty-five minutes
Not every zone is a whole hour from UTC. India (Asia/Kolkata) is UTC+5:30 year-round. Iran uses a 30-minute offset. Nepal is UTC+5:45. Newfoundland is UTC−3:30 or UTC−2:30 with DST. When either city uses a fractional offset, the gap is printed with two decimal hours so 5.50 or 10.75 does not get rounded into a wrong meeting plan.
The result also notes when the gap is not a whole hour. That sentence is easy to skip and expensive to ignore. A “five hour” assumption between London and Mumbai is wrong by thirty minutes. Write the decimal into the invite or convert it to hours and minutes before you tell a colleague when to dial.
Fractional offsets do not imply fractional workdays. They only describe the conversion. A Mumbai morning standup can still last thirty minutes; it simply starts at a London clock time that is not a round hour.
Ahead, behind, and same offset
“Ahead” means the first city’s clock shows a later civil time at the comparison instant. Tokyo is ahead of Los Angeles by a large margin most of the year. “Behind” is the opposite. Same offset means the two clocks agree on the hour and minute at that instant, even if the city names differ, as with many US Mountain locations that do not observe DST versus neighbors that do not on some dates.
Same offset is not the same city and not the same legal jurisdiction. Phoenix and a DST-observing Mountain city match in winter and diverge in summer. Recalculate across a March date if the pair includes Arizona. The meeting planner is still the right next step when you have a clock time to place, because a gap of zero hours still leaves you choosing a human-friendly hour.
Not a meeting overlap finder
A meeting planner asks when both offices are awake. This page does not. It will happily report that Auckland is twenty-one hours ahead of Chicago without suggesting 7:00 AM as a compromise. If the task is “find three hours when both teams can talk,” stop here after you understand the gap and continue on the planner. If the task is “how wrong is my mental math for this pair on 15 March,” this page is the shorter path.
Event conversion (their 9:00 AM on a named date becomes my local clock) is a third job. Difference is a scalar. Conversion is a timestamp in two zones. Mixing them causes off-by-one-day errors when the converted wall time crosses midnight. Keep the scalar here; convert wall times on an event-time or planner page.
Duration of a shift after the call, in one city’s clock, belongs on the hours calculator or the time calculator. Those tools do not ingest IANA pairs.
Date line and weekday traps
A 16-hour gap can place one city on Tuesday while the other is still on Monday. The hours-apart figure does not print weekdays. After you know the gap, check a calendar for each city if the weekday matters for a market open or a religious observance. The yearly calendar 2026 and holidays 2026 list help when one side is closed.
Airline itineraries sometimes quote local departure and local arrival without stating the gap. Computing the pair here on the flight date is a quick sanity check that a “two hour” hop that lands “five hours later” crossed zones rather than sitting on the tarmac. Cargo and broadcast schedules use the same check.
Do not subtract time-zone abbreviations from each other on paper. EST minus GMT is not a well-defined operation when one side has already sprung forward. Always go through IANA names and a date.
Related tools
Detect this browser’s own zone on the timezone detector. Watch many cities on world clock. Place a shared hour on the meeting planner. Browse other clocks from the time tools hub.
Frequently asked questions
What does the hours-apart figure mean for two cities?
It is the difference between the two IANA offsets at one shared instant on the date you picked. The sentence states whether the first city is ahead of, behind, or aligned with the second. The absolute gap does not change if you swap the pickers; only the wording of ahead versus behind reverses.
When should the comparison date be changed for DST?
Change the date whenever the call, flight, or contract falls on another civil day, especially in March, October, or November, and during southern-hemisphere summer. The United States and Europe do not switch clocks on the same weekend, so a remembered winter gap can be wrong by an hour on a spring date.
How are thirty-minute and forty-five-minute offsets handled?
The gap is printed in decimal hours so a 30- or 45-minute zone is not rounded to a whole hour. India, Nepal, Iran, and Newfoundland are common examples. The result also notes when the gap is not a whole hour. Convert that decimal to hours and minutes before you tell someone when to dial.
Why is this page different from a meeting overlap planner?
This page returns a single offset gap. A meeting planner looks for hours when both offices are typically awake and can talk. A 16-hour gap does not suggest a compromise start time. Use the planner after you understand the gap if the task is finding a shared slot rather than measuring distance.
Is the gap always a whole number of hours?
No. Any pair that includes a 30- or 45-minute IANA offset produces a fractional gap. Even two whole-hour zones can show a fractional result if you misread the decimal display, so read the note that states whether the gap is whole. Recalculate after correcting city names if a fraction looks unexpected.
How do I read which city is ahead on that date?
Ahead means the first city’s civil clock shows a later time at the comparison instant (12:00 UTC on the chosen date). Tokyo is ahead of Los Angeles by many hours most of the year. Same offset means the clocks agree at that instant; it does not mean the cities share a weekday near the Date Line.