Convert a date to ISO 8601

One unambiguous way to write a date

Is 03/04/2026 the third of April or the fourth of March? It depends on who wrote it. ISO 8601 exists to end that confusion: it writes dates from the largest unit to the smallest, year, month, day, hour, so that 2026-04-03 can only mean one thing, and it sorts correctly as plain text. It is the format used by APIs, databases, log files, configuration files and international standards. This tool converts dates written in other ways into it.

What it understands

• ISO forms already, including the basic form without dashes and with or without a time zone.
• Day/month/year and month/day/year with slashes, dots or dashes, with a choice of which comes first, and an optional time in 12- or 24-hour style.
• Dates with month names, in English or Spanish, such as Sep 21, 2026 10:30 PM or 21 de septiembre de 2026.
• ISO week dates such as 2026-W38-1 and ordinal dates such as 2026-264.
• Unix timestamps in seconds or milliseconds.

The forms you get

The result shows the moment in UTC, ending with the letter Z, which is the safest form to exchange; the same moment with your own time zone offset; the date on its own; the week date, made of the ISO year, the week and the weekday; the ordinal date, made of the year and the day of the year; the basic form, without separators, handy for file names; and the Unix timestamp. Each one has its own copy button.

Time zones

A time written with an offset or with Z is taken exactly as given. A time with no zone, such as 10:30, is ambiguous, so you choose whether to read it as your local time or as UTC. Dates without a time are treated as calendar dates and shown without conversion, so they never shift by a day.

ISO durations

ISO 8601 also defines durations, which start with the letter P: P3Y6M4DT12H30M5S means 3 years, 6 months, 4 days, 12 hours, 30 minutes and 5 seconds, and PT1H30M is one and a half hours. Enter one and the tool explains it in words and gives the total in seconds and hours, using average month and year lengths when those units are present.

What it does not do

Ambiguous dates depend on the day-first setting, so check that it matches your source. Two-digit years are not accepted, since they are too ambiguous. The tool does not name time zones by city. For that, use the time zone converter.