Time zone converter

The time box reads an hour with optional minutes and seconds — 10, 10:30, 10.30, 1030, 22:30:15 — or noon and midnight, with an optional am or pm. With am or pm the hour is 1 to 12 and 12am is midnight; without, it is 0 to 23, and 24:00 is refused rather than rolled into the next day. After the time you may name the zone: a common abbreviation (PT, PST, PDT, MT, CT, ET, AKT, HST, UTC, GMT, BST, WET, CET, EET, MSK, IST, SGT, HKT, JST, KST, AWST, ACST, AEST, NZST and their summer forms), an offset such as UTC+2, GMT-5 or +05:30, or a zone name such as Europe/Rome. A zone typed there wins over the From buttons, and the page says so. Input over 100 characters is refused; a time needs far less.

Abbreviations are loose in the wild, so each one stands for a place, not an offset: PST, PDT and PT all mean Pacific time, whichever of the two is in force on the date. When the letters name the other half of the year — PST written for a date in summer — the page reads it as Pacific time and says what it assumed, and UTC-8 gives the fixed offset instead. CST is taken as US Central and IST as India, and both say the other places they can mean. GMT is read as UTC+0, which is the UK only in winter.

Zone rules come from this browser's copy of the IANA time zone database, through Intl.DateTimeFormat with a timeZone. To find the instant, the page reads the zone's offset at a first guess, moves by it, and reads again. A wall-clock time the clocks skip when they go forward is moved on by the length of the jump, and a time that happens twice when they go back takes the first of the two — the same choices as Temporal's "compatible" mode — and both are named on the page with the other reading. Offsets are worked out to the second, so dates before standard time zones come out right as far as the database knows them.

Your own zone comes first, from Intl.DateTimeFormat().resolvedOptions().timeZone, then the zone you converted from if it is not in the list, then twelve common zones. Each row gives the time, the date in this browser's language, how many calendar days it sits ahead of or behind the date you typed, and the offset. The abbreviation after a place — PDT, CEST — is printed only when the offset is that place's present standard or summer offset. Copy copies the ISO 8601 form with offset. The date field starts on today's date on this device; nothing else here reads the clock unless you press Now. Nothing is uploaded: there is no server in this file.

The Dark button remembers its setting in this browser's local storage. Nothing you type or drop into the page is stored.