🧮 Time Zone Difference Calculator: Time Difference Between Cities (US)

Easily convert time between U.S. cities, view UTC offsets, daylight saving status, and find overlapping business hours for any date. Free and accurate.

Last updated: 19 October 2026

Time Zone Difference Calculator

This time zone calculator shows the time difference between two places on a date you choose, converts a clock time from one zone to another, flags daylight saving time and day changes, and works out when both sides are actually free. It is a time difference calculator for planning, not a live clock: nothing is uploaded, every conversion runs inside your browser.

Short answer

Pick two zones, a date and a time. You get the time zone difference in hours and minutes at that instant, the converted local time and date in the other zone, both UTC offsets and daylight saving status, a day-change flag, and the business hours overlap. The gap is calculated for the date you enter, so it is the time difference between cities you are actually looking at, not a fixed number that is copied from a table.

Privacy: the calculation runs on your device. Your zones, date and time are never sent to a server and are never stored unless you tick the optional remember box inside the form, which you can clear at any time.

The calculator

Choose the two places, the date and the time in the first zone. Results update when you press Calculate.

Locations

The local time you are typing in.

The destination zone of the conversion.

Date and time in Zone A

Format: year-month-day, the date as Zone A will show it.

Accepts AM/PM or 24-hour entries such as 14:30.

Only matters on fall-back dates, when the clock repeats an hour.

Business hours (optional)

Windows are local to each zone. The default 09:00 to 17:00 is a common office day, not a legal standard.

Your result

Result state: Estimate with limitations

Choose two zones and press Calculate.

0 hours

Time zone difference (Zone B minus Zone A) at the instant you entered.

Time zone converter output

Local time in Zone B

—

—

Day change

Day change across time zones

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Compared with the calendar date you entered in Zone A.

Zones and abbreviations

Time zone abbreviations

  • Zone A—
  • Zone B—

UTC offset

  • Zone A—
  • Zone B—

Daylight saving status

Is daylight saving time in effect

  • Zone A—
  • Zone B—

—

What this result does not do

  • It is not an official clock, not legal or contractual timekeeping, and not a guarantee of accuracy.
  • It does not model leap seconds, historical calendar changes, military or aviation time conventions, or anything other than the Gregorian calendar.
  • It does not check whether a rule changed after your browser downloaded its time zone database.
  • Non-US locations are supported from the same database but are marked as estimates with limitations.

What would change this result

  • Press Calculate to see the next daylight saving changeover for each zone.

Move the date across either zone’s changeover and the gap shifts by an hour. Arizona and Hawaii stay on standard time all year in the database used here, which is why their gaps differ from neighbouring states.

Copy-ready summary

Press Calculate to build a sentence you can paste into an email or calendar invite.

Time zone meeting planner

Time zone overlap: —

Zone A working window

—

Zone B working window

—

This business hours overlap calculator writes the same window in plain text, so it can be read aloud or pasted into a note.

How to convert time between time zones

  1. Pick Zone A. This is the zone whose clock you are reading from: your city, or the place a meeting is anchored to.
  2. Pick Zone B. This is the zone you are converting to. The Swap button reverses the pair without retyping anything.
  3. Enter the date in Zone A. The date matters: the same pair of cities can sit a whole hour apart on one date and not on another.
  4. Enter the time in Zone A. If a spring-forward gap or a fall-back repeat touches that wall time, the tool refuses it or asks which occurrence you meant.
  5. Press Calculate. You get the gap in hours and minutes, the converted time and date, both UTC offsets, the daylight saving status, the day-change flag and the business hours overlap.

How the calculation works

The tool never subtracts a fixed number of hours. It rebuilds the exact instant you meant, then measures that instant in both zones.

difference = offsetB(t) − offsetA(t)

  • t — the single instant in UTC that corresponds to the local date and time you typed in Zone A.
  • offsetA(t) — Zone A’s UTC offset, in minutes, measured at that same instant (for example −240 for EDT).
  • offsetB(t) — Zone B’s UTC offset, in minutes, at the same instant (for example +60 for BST).
  • difference — the signed gap in minutes, converted for display into hours and minutes with no rounding: 630 minutes shows as 10 hours 30 minutes.

localB = t + offsetB(t)

Worked by hand: build the instant from Zone A’s wall time, add Zone B’s offset to that instant, and read the resulting wall time. The page does the same thing with the JavaScript Intl.DateTimeFormat API and the IANA time zone database that ships with your browser, so there is no network call and no library. Offsets are exact minutes, so half-hour and 45-minute zones are shown exactly rather than rounded.

Note: the abbreviations shown (EST, EDT, PST, PDT and similar) are read for the date you entered, so they follow daylight saving time instead of being printed as a fixed label.

Worked example: Eastern Time to Pacific Time converter and four other pairs

Every number below is a hypothetical input used to test the arithmetic. The dates are real calendar dates; the outputs are what this engine produces from the IANA database on your machine.

Hypothetical fixtures: input in Zone A, converted output in Zone B, and the gap at that instant
Scenario Zone A input Zone B output Gap (B − A) Why
New York to Los Angeles, October 18, 2026 12:00, EDT, UTC-4 09:00, PDT, UTC-7 3 hours behind Both coasts on daylight time, so the usual 3-hour gap holds.
New York to London, October 18, 2026 12:00, EDT, UTC-4 17:00, BST, UTC+1 5 hours ahead Both sides on daylight time.
New York to London, October 28, 2026 12:00, EDT, UTC-4 16:00, GMT, UTC+0 4 hours ahead The database has the UK back on standard time while the US is still on daylight time.
Phoenix to Los Angeles, July 15, 2026 12:00, MST, UTC-7 12:00, PDT, UTC-7 0 hours Arizona stays on standard time all year; California does not.
Phoenix to Los Angeles, January 15, 2026 12:00, MST, UTC-7 11:00, PST, UTC-8 1 hour behind In winter both are on standard time, so the gap reappears.
Chicago to Kolkata, October 18, 2026 12:00, CDT, UTC-5 22:30, IST, UTC+5:30 10 hours 30 minutes ahead The offset is not a whole hour and is never rounded.
Los Angeles to Tokyo, October 18, 2026 22:00, PDT, UTC-7 14:00 on October 19, JST, UTC+9 16 hours ahead The day changes; the result shows the next-day date.

Substitution, step by step

Example A — Eastern time to Pacific time converter, hypothetical: 12:00 on October 18, 2026 in America/New_York, converted to America/Los_Angeles.

  1. Read the wall time as a provisional UTC value: 2026-10-18 12:00.
  2. Look up Zone A’s offset at that instant: offsetA = −240 minutes (EDT, UTC-4).
  3. Build the true instant: t = 12:00 + 240 minutes = 16:00 UTC.
  4. Look up Zone B’s offset at t: offsetB = −420 minutes (PDT, UTC-7).
  5. Difference: −420 − (−240) = −180 minutes = 3 hours behind.
  6. Converted time: 16:00 UTC + (−420 minutes) = 09:00 on October 18, 2026 in Los Angeles. Same calendar date, so no day change.

Example B — half-hour offset, hypothetical: 12:00 on October 18, 2026 in America/Chicago converted to Asia/Kolkata gives offsetA = −300, offsetB = +330, so difference = 330 − (−300) = 630 minutes = 10 hours 30 minutes, and 17:00 UTC + 330 minutes = 22:30 the same day.

About the phrase “EST to PST”: in winter New York is EST and Los Angeles is PST, three hours apart. From the first switch in March both move together, so it becomes EDT and PDT and the gap stays three hours. The label always follows your date, which is why the tool prints EDT or EST for October instead of a fixed EST. A Pacific time to Eastern time shift is the same arithmetic with the sign reversed: add 3 hours.

These are worked teaching examples with hypothetical inputs, not a claim that any particular date’s rule has been independently verified.

Comparison: the same pair of cities, four dates

The time difference between two cities is not a number you can memorise: the same pair sits a whole hour apart depending on which side of a changeover your date falls.

New York and London on hypothetical dates: the gap is not a constant
Date New York London London minus New York What changed
January 15, 2026EST, UTC-5GMT, UTC+0+5 hoursBoth on standard time.
March 15, 2026EDT, UTC-4GMT, UTC+0+4 hoursUS already on daylight time, UK not yet.
October 18, 2026EDT, UTC-4BST, UTC+1+5 hoursBoth on daylight time.
October 28, 2026EDT, UTC-4GMT, UTC+0+4 hoursUK already back on standard time, US not yet.

Both rows in the middle of the year are the same two cities and the same clock reading — only the date differs. This is the trap behind almost every scheduling mistake.

Comparison: gaps measured from Eastern Time

US time zones reference: gap from Eastern Time on a winter date and a summer date (hypothetical, read from the IANA database)
Zone January 15, 2026 July 15, 2026 Note
Central Time (Chicago)1 hour behind1 hour behindBoth zones switch on the same US dates.
Mountain Time (Denver)2 hours behind2 hours behindBoth zones switch on the same US dates.
Arizona (Phoenix)2 hours behind3 hours behindArizona does not move its clocks, so the summer gap widens.
Pacific Time (Los Angeles)3 hours behind3 hours behindBoth zones switch on the same US dates.
Alaska Time (Anchorage)4 hours behind4 hours behindBoth zones switch on the same US dates.
Hawaii Time (Honolulu)5 hours behind6 hours behindHawaii stays on standard time all year.

Values are calculator conventions read from the browser’s time zone database on the two dates shown.

US time zones at the date you entered

These seven rows are read live from the same database the calculator uses, so the abbreviations and offsets always match the date in the form above.

US time zones: UTC offset and abbreviation for the selected date
Zone IANA zone used UTC offset Label on that date Daylight saving time
Press Calculate to fill this table.

Text alternative: for any selected date the table lists each US zone, its IANA identifier, its UTC offset in hours and minutes, the abbreviation the browser reports, and whether daylight saving time is in effect on that date. Arizona and Hawaii report no daylight saving time in any row.

The gap across the year, at a glance

New York to London on five hypothetical dates: how many hours difference
January 15, 2026 (both standard) 5 hours
March 15, 2026 (US switched, UK not yet) 4 hours
April 12, 2026 (both on daylight time) 5 hours
October 18, 2026 (both on daylight time) 5 hours
October 28, 2026 (UK switched back, US not yet) 4 hours
A horizontal scale marked zero, two, four and six hours. 0 h 2 h 4 h 6 h

Text alternative: every date falls at either four or five hours. The two four-hour rows are the weeks when only one side of the Atlantic is on daylight saving time; the three five-hour rows are the weeks when both sides are on the same setting.

What the tool is built to do

From a wall time in one zone to a wall time in another, through a single UTC instant
Three boxes: Zone A time you typed, one instant in UTC, and the converted Zone B time, joined by arrows. Below them, difference equals offset B minus offset A. Zone A time you typed Instant t in UTC Zone B time converted difference = offset B(t) minus offset A(t)

✓ Included

  • Gap in hours and minutes for the exact date you entered, with no rounding.
  • Converted time, converted date and an explicit day-change flag.
  • Both UTC offsets, both abbreviations and both daylight saving states.
  • Business hours overlap written in both zones, plus a copy-ready sentence.
  • Refusal of a nonexistent local time and a choice between two occurrences.

✗ Not included

  • No official, legal or contractual timekeeping and no accuracy guarantee.
  • No live ticking clock, no current-time-in-city lookup, no world clock or map.
  • No leap seconds, no historical calendars, no military or aviation conventions.
  • No server, no account and no tracking of the places you type.
  • No independent verification of legal changeover dates.

Text alternative: your entry in Zone A is converted to one instant in UTC, both offsets are read at that instant, and their difference is the gap shown for Zone B. Everything else on this page follows that single rule.

Schedule a meeting across time zones

Used as a meeting time zone converter, the page answers one question first: when is a slot that is inside working hours on both sides? Leave both windows at 09:00 to 17:00, press Calculate, and the overlap panel returns the shared window written twice — once in Zone A’s clock and once in Zone B’s — with its length in hours and minutes.

  • Anchor the meeting on the side that has the stricter calendar, usually the client or the broadcast time.
  • Read the shared window in both zones and pick a start time that leaves room before the earlier closing time.
  • Check the day-change flag before writing the invite: a 09:00 start on one side can land on the next calendar day on the other.
  • Send the sentence from the summary box so both sides see the same wording.

The window is a planning convention, not a rule. Some teams keep a 08:00 start or a 16:00 finish, and shift work, on-call rotations and broadcast schedules follow their own patterns.

Common mistakes when you work out a time difference

Subtracting the same number of hours all year

A gap copied from a table in January can be wrong in July. Always recalculate for the date the event happens, because the offset depends on the instant, not on the month you remember.

Forgetting the two countries change clocks on different dates

For a few weeks each spring and autumn the United States and the United Kingdom are on different settings, so the same pair of cities sits one hour apart from its usual value. The comparison table above shows both weeks.

Treating EST and EDT as the same thing

EST is UTC-5 and EDT is UTC-4. An email that says 3:00 EST in July is off by an hour from what the recipient expects. Use the label the tool prints for your date.

Ignoring Arizona and Hawaii

Both stay on standard time all year in the database used here, so their gaps from other states change by an hour in summer even though nothing changed in their own offices.

Picking a local time that does not exist, or that exists twice

On the spring-forward date the clock skips an hour; on the fall-back date it repeats one. The tool refuses the first case and asks which occurrence you meant for the second instead of quietly moving your meeting.

Assuming every offset is a whole number of hours

India is 5 hours 30 minutes ahead of UTC and parts of Australia are 45 minutes ahead. This calculator reports exact minutes, so 630 minutes is shown as 10 hours 30 minutes, never as 10 or 11.

Frequently asked questions

How many hours difference between New York and London?

It depends on the date you enter. With the tool above, 12:00 on October 18, 2026 in New York converts to 17:00 the same day in London, so London is 5 hours ahead. The same input on October 28, 2026 converts to 16:00, so London is only 4 hours ahead, because the zone database in your browser has the United Kingdom on standard time while the United States is still on daylight saving time. Enter your own date for the exact gap. So the short answer to what is the time difference between New York and London is: 4 or 5 hours, and it changes twice a year. Reference starting points to check yourself: time.gov and iana.org/time-zones .

Does daylight saving time change the time difference?

Yes, whenever only one of the two locations is on daylight saving time. Because the United States and other countries change their clocks on different dates, the gap between the same two cities can be one hour larger or smaller for a few weeks in March and October. This calculator does not hard-code any changeover date: it reads the rule for the date you enter from the IANA time zone database inside your browser. The widely cited US schedule, second Sunday in March to first Sunday in November under the Uniform Time Act as amended, is a candidate rule; confirm it at uscode.house.gov and transportation.gov before relying on it.

Why does Arizona show a different gap than other Mountain states?

Most of Arizona runs on the IANA zone America/Phoenix, which stays at UTC-7 all year in your browser database, while Mountain locations that observe daylight saving time move to UTC-6 in summer. Hawaii, Pacific/Honolulu, likewise stays on standard time year-round. The result panel shows the zone name and UTC offset it actually used, so you can see the exception instead of assuming one rule for the whole country.

What happens if I enter a local time that does not exist?

On a spring-forward date the local clock skips ahead, so a wall time inside the gap does not exist. This calculator refuses to convert it and explains why, instead of silently shifting the value. On a fall-back date the same wall time occurs twice; the tool uses the first occurrence by default and lets you choose the second one.

Is this an official time source?

No. Every calculation runs in your browser using the JavaScript Intl API and the IANA time zone database version shipped with your browser, which can lag legal changes. Official US civil time is published by NIST at time.gov, and standard time zone boundaries are administered by the US Department of Transportation. This page is not endorsed by any government agency, claims no guaranteed accuracy, and is not an official or legal timekeeping source.

Can I use this to plan a meeting across time zones?

Yes. Set both business-hours windows, default 09:00 to 17:00 local, and the overlap finder returns the shared window in both zones, the length of the time zone overlap, and whether the day changes. It is a planning aid: agreements, contracts and broadcast schedules may follow a different convention.

Glossary

UTC offset
How far a zone’s clock sits from UTC, in hours and minutes, written with a sign. UTC-4 means the local clock reads four hours behind UTC. The result card prints this value for both zones so you can compare them side by side.
Wall time
The date and time printed on a clock in one place. Two places can show the same wall time while referring to different instants, which is why the tool always converts through one shared instant.
Instant (t)
A single point on the universal timeline, stored as UTC. Every result on this page is measured at one instant, so both zones are compared at the same moment.
Daylight saving time
The part of the year in which a zone advances its clock by an hour. Start and end dates differ by country and are read from the IANA time zone database rather than hard-coded.
Standard time
The setting a zone uses outside daylight saving time, for example EST rather than EDT.
Time zone abbreviations
Short labels such as EST, EDT, CST, MST, PST and PDT. They are zone-specific and date-specific: the same city uses two different labels across the year.
Time zone overlap
The span of time that falls inside both parties’ working windows at the same instant, expressed once in each zone’s clock.
Nonexistent and ambiguous local times
A wall time inside a spring-forward gap does not exist; a wall time inside a fall-back repeat occurs twice. The tool refuses the first and asks about the second.
IANA time zone database
The shared, regularly updated set of zone rules used by browsers and operating systems. Its version on your device is the version this page uses.

Method and sources

  • Last updated: October 19, 2026.
  • Calculation method: JavaScript Intl.DateTimeFormat with the IANA time zone database embedded in your browser. No library, no network request, no server-side clock.
  • Reference starting points for readers transportation.gov — US Department of Transportation, which administers standard time zones and daylight saving time; ecfr.gov — 49 CFR Part 71, standard time zone boundaries; uscode.house.gov — 15 U.S.C. section 260a, daylight saving time; time.gov — official US civil time from NIST and the US Naval Observatory; iana.org/time-zones — IANA Time Zone Database.
  • Privacy: everything runs on your device. Nothing you type is transmitted or stored unless you switch on the optional remember box, which you can clear with one button.
  • Errors can be reported through Varnda’s published contact route on varnda.com.
  • Review status: written by the Varnda Editorial Team.

Limitations and assumptions

  • Rules come from your browser’s time zone database, which can lag legislative changes; treat every result as an estimate with limitations rather than an official statement.
  • US locations are the primary supported set; other countries are supported from the same database and are labelled as estimates with limitations.
  • Dates before the database’s reliable range, future legislative changes, leap seconds, military and aviation conventions, and calendars other than Gregorian are out of scope.
  • Business hours default to 09:00–17:00 in each zone. That is a calculator convention, not an employment or labour rule.
  • No accuracy guarantee, no official status and no government endorsement is claimed or implied.

In summary

A time zone difference is a property of one date, not a fixed number. Enter the two places and the date you care about, read the gap, the converted time, both UTC offsets and the daylight saving status, then take the copy-ready sentence straight into your invite. For anything contractual or official, confirm the rule at time.gov, transportation.gov or your own local authority.

Back to the calculator

Time Zone Difference Calculator: Time Difference Between Cities (US)
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