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Find the hour that's reasonable for everyone.

Add the cities in your meeting and drag across the day. Each row shows local time, with working hours highlighted, so the overlap is obvious. Daylight-saving changes are handled for the date you pick.

Tue 29 Sep 2026Mon 26 Oct 2026Mon 15 Mar 2027

4 of 8 cities

hours in London

0003060912151821

LondonUTC+114:00same day

01234567891011121314151617181920212223

New YorkUTC−409:00same day

19202122230123456789101112131415161718

DelhiUTC+5:3018:30same day

45678910111213141516171819202122230123

SingaporeUTC+821:00same day

78910111213141516171819202122230123456

working hours 9-17early or late 7-9, 17-22nightdrag across the hour row, or click a suggestion below

scheduleworkable, not idealLondon 14:00 is outside working hours in Delhi, Singapore.There is no hour when all 4 cities are working. The suggestions spread the inconvenience as fairly as possible.

least-bad times

12:00London12:00New York07:00Delhi16:30Singapore19:0014:00London14:00New York09:00Delhi18:30Singapore21:0013:00London13:00New York08:00Delhi17:30Singapore20:00

~/the-gap-moves

London and New York are 5 hours apart. Except when they're 4.

The US and Europe change their clocks on different weekends, so for a few weeks each spring and autumn the usual gap shrinks by an hour. Recurring meetings drift without anyone noticing. Pick a pair to see the whole year.

London ↔ New YorkLondon ↔ SydneyBerlin ↔ São Paulo

JanFebMarAprMayJunJulAugSepOctNovDec

usual gap5 hoursgap ranges4-5 hweeks off-pattern4

Darker bars are the weeks in March and late October/early November when only one side has changed its clocks.

~/not-whole-hours

Four places that break the "whole hours" assumption.

Most zones sit a whole number of hours from UTC, but not all. Calendars and scripts that round to the hour book these people 30 or 45 minutes late. Each card shows the current local time from the planner above.

IndiaUTC+5:3018:30One zone for the whole country, set half an hour off.

NepalUTC+5:4518:45Fifteen minutes ahead of India, one of only two :45 zones.

Adelaide+9:30 / +10:3022:30Half-hour offset and daylight saving, so the gap to Sydney is always 30 minutes.

Newfoundland−3:30 / −2:3010:30Half an hour ahead of Atlantic Canada all year.

~/say-it-once

Copy the time in a way nobody can misread.

Your chosen meeting time, written for every city in the planner, in the formats people actually paste into invites and code.

everyoneLondon 14:00 · New York 09:00 · Delhi 18:30 · Singapore 21:00content_copyCopy

ISO 8601 · UTC2026-09-29T13:00:00Zcontent_copyCopy

with offset2026-09-29T14:00+01:00content_copyCopy

Unix timestamp1790686800content_copyCopy

~/a-zone-is-a-history

A time zone is not an offset. It’s every offset a place has ever used.

An IANA name like Europe/London stands for a full record of local clock changes since local mean time ended. This scans that record as your browser ships it, week by week from 1850 to 2035, and pins each change to the second. Each column is one year: its height shows the spread between winter and summer offsets.

LondonApiaMoscowPyongyangSão PauloCasablancaKolkataKiritimatiYour zone

nowUTC+1British Summer Time

transitions 1850-2035236found in 80 ms, each pinned to the second

distinct offsets3116 years with a seasonal change

next change2026-10-25 01:00ZUTC+1 → UTC+0

Europe/Londonbottom UTC+0 · top UTC+2

18501896194319892035

one offset all yearseasonal change (winter to summer span)today

Notable changes4 of 236 transitions

1916-05-21 02:00ZUTC+0 → UTC+1arrow_upwardclocks forward +1 h

1941-05-04 01:00ZUTC+1 → UTC+2arrow_upwardclocks forward +1 h

1945-10-07 02:00ZUTC+1 → UTC+0arrow_downwardclocks back 1 h

1971-10-31 02:00ZUTC+1 → UTC+0arrow_downwardclocks back 1 h

London · Europe/LondonBritain left local mean time for railway time in 1847, ran double summer time in the 1940s, and stayed on +1 all year as British Standard Time from 1968 to 1971.

Pre-1970 records come from the tz database copy built into your browser. Some builds merge zones that have agreed since 1970, so very old entries can differ between browsers. Offsets are measured with Intl.DateTimeFormat; nothing is hard-coded.

~/every-zone-right-now

Every zone your browser knows, measured this minute.

Intl.supportedValuesOf lists the IANA zones this browser supports. Each is grouped by its current offset; half- and quarter-hour offsets are darker. Click a bar to list its zones. Offsets run from 12 hours behind UTC to 14 ahead, so for part of every day three calendar dates are in use at once.

zones418from Intl.supportedValuesOf

distinct offsets37in use this minute

non-whole-hour14zones at :30 or :45

span25 hUTC−11 to UTC+14

dates in use2calendar days somewhere right now

−11−10−9:30−9−8−7−6−5−4−3−2:30−2−10+1+2+3+3:30+4+4:30+5+5:30+5:45+6+6:30+7+8+8:45+9+9:30+10+10:30+11+12+13+13:45+14

UTC+3: 42 zones

Africa/Addis_AbabaAfrica/AsmeraAfrica/CairoAfrica/Dar_es_SalaamAfrica/DjiboutiAfrica/KampalaAfrica/MogadishuAfrica/NairobiAntarctica/SyowaAsia/AdenAsia/AmmanAsia/BaghdadAsia/BahrainAsia/BeirutAsia/DamascusAsia/FamagustaAsia/GazaAsia/HebronAsia/JerusalemAsia/KuwaitAsia/NicosiaAsia/QatarAsia/RiyadhEurope/AthensEurope/BucharestEurope/ChisinauEurope/HelsinkiEurope/IstanbulEurope/KievEurope/KirovEurope/MariehamnEurope/MinskEurope/MoscowEurope/RigaEurope/SimferopolEurope/SofiaEurope/TallinnEurope/VilniusEurope/VolgogradIndian/AntananarivoIndian/ComoroIndian/Mayotte

dates in use nowSat 10 Oct · 201 zonesSun 11 Oct · 217 zones

Abbreviations are not identifiersSame letters, different places, with offsets right now. The last column is what this browser’s Date.parse does with “15 Jan 2026 12:00:00 CST” and so on.

CSTUS CentralUTC−5ChinaUTC+8CubaUTC−4read as UTC−6

ISTIndiaUTC+5:30Irish Standard (summer)UTC+1IsraelUTC+3rejected (NaN)

BSTBritish SummerUTC+1BangladeshUTC+6rejected (NaN)

ASTAtlanticUTC−3ArabiaUTC+3rejected (NaN)

ESTUS EasternUTC−4Australian Eastern (older usage)UTC+11read as UTC−5

PSTUS PacificUTC−7PhilippineUTC+8read as UTC−8

GSTGulfUTC+4South GeorgiaUTC−2rejected (NaN)

Names, links and renamesWhat this browser does with each name: the ID it resolves to, whether it’s in the supported list, and the offset now.

Asia/CalcuttaOld spelling; a link to Asia/Kolkata since 2008.Asia/Calcuttain supported list+5:30

Asia/KolkataCanonical tzdb name.Asia/Calcuttanot in supported list+5:30

US/EasternBackward-compatibility link to America/New_York.America/New_Yorknot in supported list−4

Europe/KievRenamed Europe/Kyiv in tzdb 2022b.Europe/Kievin supported list+3

Europe/KyivCanonical since 2022b; older browsers may reject it.Europe/Kievnot in supported list+3

GBLegacy link to Europe/London.Europe/Londonnot in supported list+1

Etc/GMT+5POSIX sign convention: this means UTC−5.Etc/GMT+5not in supported list−5

EST5EDTPOSIX-style zone; a link to America/New_York since tzdb 2024b.America/New_Yorknot in supported list−4

America/Buenos_AiresLink to America/Argentina/Buenos_Aires.America/Buenos_Airesin supported list−3

Etc/UTCtzdb’s canonical UTC; ECMA-402 reports it as UTC.UTCnot in supported list0

Mars/Olympus_MonsNot a zone: should throw RangeError.RangeErrornot in supported list-

~/store-the-zone-not-the-offset

A weekly meeting, saved two ways, drifts two ways.

The planner’s meeting, repeated weekly. Saved with the organiser’s zone (iCalendar TZID), it stays at the same wall-clock time for the organiser and moves for everyone else when clocks change. Saved as a fixed UTC instant, it moves for everyone, organiser included. The table lists only the weeks where something changes.

Repeat for26 weeks

Organiser London · 14:00 local · every Tue from 2026-09-29

London (organiser)zone-saved: steadyUTC-saved: 1 shift

New Yorkzone-saved: 3 shiftsUTC-saved: 2 shifts

Delhizone-saved: 1 shiftUTC-saved: steady

Singaporezone-saved: 1 shiftUTC-saved: steady

weekLondonNew YorkDelhiSingapore

week 12026-09-2914:00 TueUTC-fixed 14:00 Tue09:00 TueUTC-fixed 09:00 Tue18:30 TueUTC-fixed 18:30 Tue21:00 TueUTC-fixed 21:00 Tue

week 52026-10-2714:00 TueUTC-fixed 13:00 Tue10:00 TueUTC-fixed 09:00 Tue19:30 TueUTC-fixed 18:30 Tue22:00 TueUTC-fixed 21:00 Tue

week 62026-11-0314:00 TueUTC-fixed 13:00 Tue09:00 TueUTC-fixed 08:00 Tue19:30 TueUTC-fixed 18:30 Tue22:00 TueUTC-fixed 21:00 Tue

week 252027-03-1614:00 TueUTC-fixed 13:00 Tue10:00 TueUTC-fixed 09:00 Tue19:30 TueUTC-fixed 18:30 Tue22:00 TueUTC-fixed 21:00 Tue

meeting.ics · RFC 5545 with VTIMEZONEcontent_copyCopydownload.ics

BEGIN:VCALENDARVERSION:2.0PRODID:-//FileFormer//Time Zone Planner//ENCALSCALE:GREGORIANBEGIN:VTIMEZONETZID:Europe/LondonBEGIN:DAYLIGHTDTSTART:20260329T010000RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SUTZOFFSETFROM:+0000TZOFFSETTO:+0100TZNAME:BSTEND:DAYLIGHTBEGIN:STANDARDDTSTART:20261025T020000RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SUTZOFFSETFROM:+0100TZOFFSETTO:+0000TZNAME:GMT+0END:STANDARDEND:VTIMEZONEBEGIN:VEVENTUID:x7sx1acb2y@fileformer.comDTSTAMP:20261010T222919ZDTSTART;TZID=Europe/London:20260929T140000DTEND;TZID=Europe/London:20260929T143000RRULE:FREQ=WEEKLY;COUNT=26SUMMARY:Team syncDESCRIPTION:Planned with the FileFormer time zone converterEND:VEVENTEND:VCALENDAR

DAYLIGHT · BSTBYDAY=-1SU in month 3Last Sunday of Mar at 01:00 local: UTC+0 → UTC+1.

STANDARD · GMT+0BYDAY=-1SU in month 10Last Sunday of Oct at 02:00 local: UTC+1 → UTC+0.

same rules as a POSIX TZ string<+00>0BST,M3.5.0/1,M10.5.0The format of the TZ environment variable, also stored in the footer of TZif files (RFC 9636) to cover dates after the last listed transition. Offsets are written west-positive, so the signs look reversed.

Rules derived from the 2 clock changes measured in 2026. Zones whose dates don’t follow an nth-weekday rule (Morocco, or any government decree) would need RDATE lines instead.

~/reference

The planner’s meeting in every zone-aware format.

Each string is built from the meeting above. The last column feeds it to this browser’s Date.parse (and Temporal, if present) and checks it returns the right instant.

formatthis meetingwhat it keepsthis browser

ISO 8601 / RFC 33392026-09-29T14:00:00+01:00The instant and the offset in force. The zone is lost, so a later recurrence can’t follow clock changes.check_circlecorrect instant

ISO 8601 basic20260929T140000+0100Valid ISO 8601, but RFC 3339 requires the extended form.cancelrejected

RFC 9557 (IXDTF)2026-09-29T14:00:00+01:00[Europe/London]Offset plus the IANA zone in brackets (2024). The format Temporal uses.check_circleTemporal: correct

RFC 5322 email dateTue, 29 Sep 2026 14:00:00 +0100Numeric offset; a legacy zone name like EST is allowed only for US zones.check_circlecorrect instant

HTTP-date (RFC 9110)Tue, 29 Sep 2026 13:00:00 GMTAlways written in GMT; no other zone is permitted.check_circlecorrect instant

iCalendar (RFC 5545)DTSTART;TZID=Europe/London:20260929T140000Wall-clock time plus zone, resolved with the VTIMEZONE in the same file.removenot a Date string

POSIX TZ<+00>0BST,M3.5.0/1,M10.5.0Only the rule, no date: standard and summer names, offsets and change days.removenot a Date string

Timeline

1 Dec 1847Most British railways adopt Greenwich time, replacing local mean time along their lines.

18 Nov 1883US and Canadian railways switch to four standard time zones.

Oct 1884The International Meridian Conference adopts Greenwich as the prime meridian.

30 Apr 1916Germany and Austria-Hungary introduce daylight saving; Britain follows within weeks.

1918The US Standard Time Act makes time zones and daylight saving federal law.

1 Jan 1972UTC takes its current form, kept within a second of Earth rotation by leap seconds.

1986Arthur David Olson starts the tz database that IANA maintains today.

2011-2012After a copyright suit (later dropped) briefly takes it offline, IANA takes over the database; RFC 6557 sets its procedures.

30 Dec 2011Samoa and Tokelau skip a calendar day to move west of the date line.

15 Aug 2015North Korea creates Pyongyang Time, UTC+8:30. It lasts until May 2018.

Mar 2019The European Parliament votes to end seasonal clock changes; EU governments never finish the law.

2024RFC 9557 adds bracketed zone names to timestamps; RFC 9636 documents the TZif file format.

Primary sources

IANA time zone databasewww.iana.org RFC 6557: procedures for the tz databasewww.rfc-editor.org RFC 9636: the TZif formatwww.rfc-editor.org RFC 5545: iCalendar (VTIMEZONE, RRULE)www.rfc-editor.org RFC 9557: timestamps with additional informationwww.rfc-editor.org RFC 3339: date and time on the internetwww.rfc-editor.org ECMA-402: time zone namestc39.es POSIX: the TZ environment variablepubs.opengroup.org

~/other-calculators

More about time.

Neighbouring tools, with a typical result for each.

scheduleTimestamp converterTurn a Unix number from a log into a readable date.1790679600arrow_forward29 Sep 2026 10:20 date_rangeDate calculatorCount working days to a deadline across time zones.today → 25 Decarrow_forward87 days event_repeatCron generatorSchedule a job; cron runs in the server’s zone, usually UTC.weekdays 9:00arrow_forward0 9 * * 1-5

Sources

[1]IANA time zone databaseThe shared source every device uses for zones and clock changes.IANA ↗[2]ISO 8601The international format for writing dates and times.ISO ↗[3]Daylight saving time by countryWho changes clocks, and when.Wikipedia ↗