Time zones

Package: TIME_PACKAGE. Registered by createEngine(); for a slimmer engine, register it explicitly (see choosing packages).

A time zone is a region that keeps the same clock: when it is nine in the morning in London it is five in the evening in Tokyo, because the two are eight hours apart. Many places also move their clocks an hour forward in spring and back in autumn, which is called daylight saving, so the gap between two places changes on the days their clocks change, and not always on the same days. Name a city, a country or a standard abbreviation and the engine looks the zone up for you, using the same zone database your operating system reads, so the answers follow whatever the rules are for the date in question.

A time in another zone

Write a time, the place it is in, and in the place you want it shown in. The answer is the time the clocks there show at that same moment.

3pm London in Tokyo // 12:00 AM (+1 day)
6pm Sydney in Chicago // 2:00 AM

On its own the line reads the time against today, so its answer can change with the calendar: a gap that is five hours this month may be four next month. The answers shown for a line without a date are for noon on Wednesday 11 March 2026 in London, the fixed moment these pages are checked against, and the notepad gives yours. Add on and a date to ask about a particular day, and the answer is fixed. The date can sit after the first place or at the end of the line.

3pm London on 23 September 2026 in Tokyo // 11:00 PM
3pm London in Tokyo on 23 September 2026 // 11:00 PM

When the date in the other place is not the date you named, the answer says by how many days it differs. Sydney is already into the next morning, and San Francisco is still on the evening before.

3pm London on 23 September 2026 in Sydney // 12:00 AM (+1 day)
9am Tokyo on 23 September 2026 in San Francisco // 5:00 PM (-1 day)

A time kept in a variable

A time you have already worked out, or will use more than once, can sit in a variable. Write the variable where the time would go, then the place that time is in and in the places to show it in. It reads the variable’s time of day and its date as a clock in the first place, exactly as the written-out time is read, and one or several places after in work the same way.

meeting = 2026-09-23T15:00 // Wednesday, September 23, 2026, 3:00:00 PM
meeting London in Tokyo // 11:00 PM
meeting London in rio de janeiro and New York // Rio de Janeiro 11:00 AM, New York 10:00 AM
(meeting + 1 hour) London in Tokyo // 12:00 AM (+1 day)

The variable has to hold a time. One that holds a number, or anything else, is refused by name rather than guessed at, since a zone has nothing to convert in it. The place after the variable must be one the engine knows and must be followed by in, so a variable whose name is a unit (t, m) or a word before an ordinary in conversion is read as it always was.

t = 5 // 5
t London in Tokyo // ERROR: A zone after a name converts the time of day it holds, as in "t London in Tokyo" with t = 3pm, and this holds a number.

Working with the answer

The answer is a time, not a piece of text, so you can keep calculating with it. Add or take away a length of time and the clock in the other place moves on, with the day shift updated to match. Write in and another place to see the same moment on that clock instead.

(3pm London on 23 September 2026 in Tokyo) + 1 hour // 12:00 AM (+1 day)
(3pm London on 23 September 2026 in Tokyo) - 30 minutes // 10:30 PM
(3pm London on 23 September 2026 in Tokyo) in New York // 10:00 AM

The day shift is always counted from the day you named, so it stays right however the time is moved. Because the answer is a value rather than text, a reader whose notes are set to another language sees it on their own clock: under German settings, 11:00 PM reads 23:00. A note written when these answers were text still works: comparing the answer with the text it used to be, or joining text to it, gives what it always gave.

(3pm London on 23 September 2026 in Tokyo) == "11:00 PM" // true
"call at " + (3pm London on 23 September 2026 in Tokyo) // call at 11:00 PM

Several zones at once

A team spread across several places rarely asks about just one of them. List the places after in, separated by commas or and, and each is answered, labelled with the name you wrote, so the answer reads as a small world clock for the moment you named.

3pm London on 23 September 2026 in Tokyo, New York and Sydney // Tokyo 11:00 PM, New York 10:00 AM, Sydney 12:00 AM (+1 day)

The day shift is measured against the date in the first place, the one whose clock you gave. An abbreviation or an offset from UTC works in the list as well as a city, and keeps its own label.

3pm JST on 23 September 2026 in EST and CET // EST 2:00 AM, CET 8:00 AM
3pm GMT+9 on 23 September 2026 in London and UTC-5 // London 7:00 AM, UTC-5 1:00 AM

A place whose name is more than one word is written with its spaces, as it is said, whether it is a city (Los Angeles, Las Vegas, Mexico City, Kuala Lumpur, New Delhi, Cape Town, Rio de Janeiro, Sao Paulo) or a country (South Africa, United Kingdom).

3pm London on 23 September 2026 in Los Angeles, Mexico City and Kuala Lumpur // Los Angeles 7:00 AM, Mexico City 8:00 AM, Kuala Lumpur 10:00 PM
3pm London on 23 September 2026 in Las Vegas // 7:00 AM
3pm London on 23 September 2026 in New Delhi // 7:30 PM
3pm London on 23 September 2026 in Cape Town // 4:00 PM
3pm London on 23 September 2026 in Rio de Janeiro // 11:00 AM
3pm London on 23 September 2026 in Sao Paulo // 11:00 AM
3pm London on 23 September 2026 in South Africa // 4:00 PM
3pm Los Angeles on 23 September 2026 in United Kingdom // 11:00 PM

A label is the name as you wrote it, with the first letter of each word raised the way the place writes its name. The small linking words inside a name, such as the de of Rio de Janeiro, keep the case you gave them, and nothing you capitalised is lowered.

3pm london on 23 September 2026 in rio de janeiro and new york // Rio de Janeiro 11:00 AM, New York 10:00 AM

Why the date matters

The clocks do not change everywhere on the same day. New York moves its clocks forward on the second Sunday of March and London on the last Sunday, so for those three weeks the two cities are four hours apart rather than five.

3pm London on 1 March 2026 in New York // 10:00 AM
3pm London on 20 March 2026 in New York // 11:00 AM
3pm London on 23 September 2026 in New York // 10:00 AM

The southern hemisphere has its summer in the northern winter, so its clocks go forward in September or October, just as the northern ones are about to go back. Sydney goes forward on 4 October 2026, while London is still on summer time.

9am Sydney on 1 October 2026 in London // 12:00 AM
9am Sydney on 5 October 2026 in London // 11:00 PM (-1 day)

On the day the clocks change, one hour is special. When they go forward, the hour they jump over never happens, and when they go back, the hour they repeat happens twice. A time inside either names no single moment, so it is refused with the reason rather than moved an hour without saying so.

1:30am London on 29 March 2026 in Tokyo // 1:30 AM did not happen in London on March 29, 2026: the clocks went forward past it
1:30am London on 25 October 2026 in Tokyo // 1:30 AM happened twice in London on October 25, 2026, when the clocks went back, so it names no single moment
2:30am London on 29 March 2026 in Tokyo // 10:30 AM

The same refusal applies to a line with no date, on the two days a year it matters.

Working hours in common

The other question a team in several zones asks is when everyone is at work at the same time. overlap of takes a stretch of the day, such as office hours, and the places, and finds the part of that stretch that falls inside it in every place at once. The answer gives the length of the shared stretch first, then where it falls on each place’s own clock.

overlap of 9am to 5pm in London and New York on 23 September 2026 // 3 hours: London 2:00 PM to 5:00 PM, New York 9:00 AM to 12:00 PM
overlap of 9am-5pm in London and New York on 23 September 2026 // 3 hours: London 2:00 PM to 5:00 PM, New York 9:00 AM to 12:00 PM

A hyphen between the two times reads the same as to here, because after overlap of a stretch of the day is what is expected. Elsewhere a hyphen between two times is read as a subtraction, not as a range, so write to there.

Each further place narrows the shared stretch to what it has in common with the others.

overlap of 9am to 5pm in London, Paris and New York on 23 September 2026 // 2 hours: London 2:00 PM to 4:00 PM, Paris 3:00 PM to 5:00 PM, New York 9:00 AM to 11:00 AM

The stretch follows daylight saving day by day. During the three weeks in March when New York has moved its clocks and London has not, the two share an hour more.

overlap of 9am to 5pm in London and New York on 20 March 2026 // 4 hours: London 1:00 PM to 5:00 PM, New York 9:00 AM to 1:00 PM

The day is the first place’s. A place on the far side of the date line keeps its matching hours on its own yesterday or tomorrow, and the answer carries the shift, so Tokyo’s morning is found against San Francisco’s afternoon before.

overlap of 8am to 6pm in Tokyo and San Francisco on 23 September 2026 // 2 hours: Tokyo 8:00 AM to 10:00 AM, San Francisco 4:00 PM to 6:00 PM (-1 day)

When the places share nothing, that is the answer. London’s working day ends at one in the morning in Tokyo, so the two only touch.

overlap of 9am to 5pm in London and Tokyo on 23 September 2026 // No overlap between London and Tokyo

Hours that end earlier than they start run past midnight, as a night shift does. Hours longer than twelve can meet another place’s twice in one day, once at each end, and both stretches are given, with the length their total.

overlap of 10pm to 6am in London and New York on 23 September 2026 // 3 hours: London 3:00 AM to 6:00 AM, New York 10:00 PM to 1:00 AM (-1 day)
overlap of 5am to 11pm in London and Tokyo on 23 September 2026 // 12 hours: London 5:00 AM to 3:00 PM, Tokyo 1:00 PM to 11:00 PM; London 9:00 PM to 11:00 PM, Tokyo 5:00 AM to 7:00 AM (+1 day)

Without on, the overlap is today’s.

overlap of 9am to 5pm in London and New York // 4 hours: London 1:00 PM to 5:00 PM, New York 9:00 AM to 1:00 PM

An overlap needs two places or more, and hours with a length, and says so when it is not given them.

overlap of 9am to 5pm in London on 23 September 2026 // An overlap needs two or more places, as in "overlap of 9am to 5pm in London and New York"
overlap of 9am to 9am in London and Paris on 23 September 2026 // 9:00 AM to 9:00 AM has no length, so no time falls inside it

What the overlap does not cover, deliberately:

• One set of hours for everyone. The hours on the line apply to every place named. Places that keep different hours, an office that opens at eight beside one that opens at ten, are not compared in one line.
• Weekends and public holidays. The hours are applied to every day, so a Monday morning in Tokyo that falls on a Sunday afternoon in San Francisco is reported like any other. Working days are a separate question, on working days.
• The answer is text. It is written to be read, not a value to do arithmetic with.

The time there now

Three forms answer about the present moment, so their answers change as you read them: the time in a place, its date, which can be a day either side of yours, and how far apart two places are right now. The answers shown are for the same fixed moment.

time in Paris // 1:00 PM
date in Vancouver // March 11, 2026
time difference between Seattle and Moscow // Moscow is 10 hours ahead of Seattle

The gap between two places is not fixed: it moves whenever either one changes its clocks. To plan for a particular day, add on and the date, and the gap is worked out for that day. London and New York change on different Sundays in March, so for three weeks they are four hours apart rather than five:

time difference between London and New York on 1 March 2027 // London is 5 hours ahead of New York on March 1, 2027
time difference between London and New York on 20 March 2027 // London is 4 hours ahead of New York on March 20, 2027
time difference between London and Tokyo on 1 July 2027 // Tokyo is 8 hours ahead of London on July 1, 2027
time difference between Tokyo and Adelaide on 1 March 2027 // Adelaide is 1 hour 30 minutes ahead of Tokyo on March 1, 2027

A date names a whole day, and on the day a place changes its clocks the gap changes partway through it. The dated answer is the gap at noon in the first place named, which is clear of every clock change in use.

time in and date in answer only for now. A line such as time in Tokyo on 1 March 2027 is refused, because the clock as it is now, carried to another day, answers nothing useful. The two questions it usually means have their own forms: a time converted on that day (2pm London in Tokyo on 1 March 2027), and the gap between two places on it, as above.

The difference as a number of hours

A time difference is how far one place’s clock is set ahead of another’s. It is written as a sentence, but it is a length of time underneath, measured from the first place you name to the second: positive when the second place is ahead, negative when it is behind. Add in hours, or in minutes, to get that length on its own, ready to use in a calculation such as moving a time from one clock to the other.

time difference between Seattle and Moscow in hours // 10 hours
time difference between Moscow and Seattle in hours // -10 hours
time difference between London and New Delhi in minutes // 330 minutes

Places that keep the same clock have a difference of nothing, and the answer says they share it rather than that one is zero hours ahead.

time difference between Paris and Berlin // Berlin and Paris currently share the same UTC offset
time difference between Paris and Berlin in hours // 0 hours

A date or a time in a zone

Writing in <zone> after a date, or after a time of day, reads it in that zone rather than in yours, and shows it there. A bare date means midnight, so 2026-04-03 in Tokyo is the day that starts in Tokyo, shown as that day.

2026-04-03 in Tokyo // Friday, April 3, 2026
3 April 2026 in New York // Friday, April 3, 2026
2026-04-03T09:00 in Tokyo // Friday, April 3, 2026, 9:00:00 AM
2026-04-03 in UTC // Friday, April 3, 2026

A time of day works the same way: 6pm in Chicago is six in the evening in Chicago, and stays a time of day.

6pm in Chicago // 6:00:00 PM

The result is a date, not a quantity. A name that is not a zone is refused rather than answered, and a unit is told apart from a misspelt zone, because the two mistakes have different fixes. A zone belongs to a date: after an ordinary number, in asks for a unit, so a city there is refused as a word that is not a unit, the same as 5 km in Tokyo.

2026-04-03 in Atlantis // "Atlantis" is not a time zone this engine knows. Name a city ("in Tokyo"), a standard abbreviation ("in JST") or "in UTC"
2026-04-03 in furlongs // A date cannot be read in "furlongs". "in <name>" after a date names a time zone, as in "2026-04-03 in Tokyo"
5 in Tokyo // "Tokyo" is not a unit.

An offset from UTC works after a date as well as a place does. An offset is the number of hours, and sometimes minutes, that a clock is set ahead of UTC or behind it: UTC-5 is five hours behind, and UTC+5:45 five and three quarters ahead. Unlike a place, an offset never changes for daylight saving, so it names a clock that stays put all year. The time is read on that clock and shown there, as a place’s is.

2026-04-03T15:00 in UTC-5 // Friday, April 3, 2026, 3:00:00 PM
2026-04-03T15:00 in GMT+9 // Friday, April 3, 2026, 3:00:00 PM
2026-04-03T15:00 in UTC+5:45 // Friday, April 3, 2026, 3:00:00 PM
2026-04-03 in UTC-05:00 // Friday, April 3, 2026

A time that already names its moment, one written with its own offset such as Z (UTC itself), or now, is moved onto the offset’s clock instead, because the moment is fixed. Three in the afternoon in UTC is ten in the morning five hours behind it.

2026-04-03T15:00Z in UTC-5 // Friday, April 3, 2026, 10:00:00 AM

UTC and GMT are read in either case, with or without a space either side of the sign. A number with a unit after it is arithmetic rather than an offset, so in UTC - 5 hours is the time in UTC less five hours. Clocks are kept from twelve hours behind UTC to fourteen ahead, so an offset outside that range, or one with sixty minutes or more, is refused rather than read as a clock that exists nowhere.

2026-04-03T15:00 in UTC - 5 hours // Friday, April 3, 2026, 10:00:00 AM
2026-04-03T15:00 in UTC+25 // "UTC+25" is not an offset a clock keeps: write whole hours and minutes from UTC-12 to UTC+14, as in "UTC-5" or "UTC+5:45"

An offset suits a clock that never changes. For a place that changes its clocks, an offset is right for only part of the year, so name the place and the answer follows its clocks through the year: write the city or its abbreviation, in New York or in Tokyo, or in JST instead. A host that wants the whole document computed in one zone can pin it: see dates on Temporal.

The names that work

• Cities and places: every place the time zone database names, about four hundred, from Kathmandu and Hobart to Apia, with names of more than one word written with spaces (Ho Chi Minh, Dar es Salaam, Port au Prince), and around ninety more cities the database has no zone of its own for, such as Mumbai and San Francisco. A place the database has renamed answers to both names: Kolkata and Calcutta, Kyiv and Kiev, Ho Chi Minh and Saigon.
• Countries, which read as their capital’s zone: Japan is Tokyo, and Australia is Sydney even though the country spans several zones.
• Standard abbreviations such as PST, EST, CET, JST and AEST. Each names a place rather than a season, so EST in July is New York’s summer time, and where an abbreviation has more than one meaning (IST is used in India, Ireland and Israel) the most common is taken, which for IST is India.
• UTC and GMT, and in the time conversions above an offset from them, GMT+9 or UTC-5:30, which is fixed and never changes for daylight saving.

A place whose name is more than one word is read whole, with a space between the words and in any case, so time in buenos aires is Buenos Aires. The database’s names of that kind, beyond those above, are Addis Ababa, Bahia Banderas, Blanc Sablon, Boa Vista, Broken Hill, Buenos Aires, Cambridge Bay, Campo Grande, Cape Verde, Ciudad Juarez, Coral Harbour, Costa Rica, Dawson Creek, El Aaiun, El Salvador, Fort Nelson, Glace Bay, Goose Bay, Grand Turk, Isle of Man, La Paz, Lord Howe, Lower Princes, Pago Pago, Phnom Penh, Port Moresby, Port of Spain, Porto Novo, Porto Velho, Punta Arenas, Rankin Inlet, Rio Branco, Rio Gallegos, San Marino, Santo Domingo, Sao Tome, South Georgia, St Barthelemy, St Helena, St Johns, St Kitts, St Lucia, St Thomas, St Vincent, Swift Current and Ust Nera.

time difference between Kathmandu and Kolkata // Kathmandu is 15 minutes ahead of Kolkata
3pm London on 1 March 2027 in Hobart // 2:00 AM (+1 day)

A few of the database’s names are left out, because reading them as a place would mislead: ordinary words (Easter, Christmas and Reunion are islands in the database), names a better-known place elsewhere holds (Cordoba is in Spain as well as Argentina, and San Juan reads as Puerto Rico rather than the Argentine province), and the Antarctic research stations, several of which are named after people. Each is listed, with its reason, in the generator that builds the table.

The full identifiers of the zone database, such as Asia/Tokyo, cannot be typed directly, because the slash reads as division, and a hyphenated name is written with spaces for the same reason: Port au Prince, not Port-au-Prince.