Developer time tools
ISO 8601 writes a date and time as YYYY-MM-DDThh:mm:ssZ in UTC, ordered from the largest unit to the smallest so the text sorts chronologically. Paste any date, ISO string, or Unix timestamp below to see every ISO representation at once: the UTC timestamp, ISO week date, ordinal date, Unix epoch, and an ISO duration to now.
Empty input shows the current UTC instant, updating live.
ISO 8601 (UTC)
2026-06-20T03:32:11Z
ISO 8601 with milliseconds
2026-06-20T03:32:11.068Z
ISO week date
2026-W25-6
Ordinal date (day of year)
2026-171
Calendar date only
2026-06-20
Time only
03:32:11
Unix timestamp (seconds)
1781926331
Unix timestamp (milliseconds)
1781926331068
Weekday
Saturday
ISO duration (from now)
P0D
Approximate: 30-day months, 365-day years
Human readable (UTC)
Saturday, June 20, 2026 at 03:32:11 AM UTC
Almost every bug involving dates comes from ambiguity. Write "06/07/2026" and half the world reads June 7 while the other half reads July 6. ISO 8601 removes that ambiguity by fixing one order, biggest unit to smallest: year, month, day, then hour, minute, second. That single rule has a powerful side effect. Because the most significant field comes first, ISO 8601 strings sort chronologically when compared as plain text, so you can order log lines, filenames, and database rows correctly without parsing them into date objects at all. Add the trailing Z and the timestamp is anchored to UTC, which means a value generated in Tokyo and a value generated in New York can be compared directly with no timezone guesswork. This is why JSON APIs, log aggregators, Git, and standards like RFC 3339 all converge on it.
ISO 8601 carries two representations that trip people up. The first is the week date, written YYYY-Www-D, for example 2026-W25-2. It counts weeks instead of months: weeks start on Monday, week 1 is the week that contains the year's first Thursday, and the final digit is the day of the week from 1 for Monday to 7 for Sunday. A consequence worth remembering is that the ISO week-numbering year is not always the same as the calendar year. The first days of January can belong to the last week of the previous year, and the last days of December can belong to week 1 of the next year. The second representation is the ordinal date, YYYY-DDD, which numbers the day within the year from 001 to 365 or 366. Both are shown above so you never have to compute them by hand for a payroll week, a sprint cadence, or a fiscal calendar.
ISO 8601 also defines durations, and they have their own grammar. A duration starts with the letter P for "period." The date portion lists years with Y, months with M, and days with D. A T then introduces the time portion, which lists hours with H, minutes with M, and seconds with S. The classic gotcha is the letter M, which means months before the T and minutes after it, so P2M is two months while PT2M is two minutes. A full example, P1Y2M10DT2H30M, reads as one year, two months, ten days, two hours, and thirty minutes. Durations are common in API payloads, video metadata, retry policies, and scheduling formats. One caveat: a duration in months or years is not a fixed number of seconds, because months vary in length and some years have a leap day, so the duration this tool derives between your input and the current moment is an approximation built on 30-day months and 365-day years. When you need exact elapsed time, use the seconds or milliseconds value, which is always precise.
Working with raw Unix time instead? The epoch converter focuses on timestamps in seconds and milliseconds with the current epoch and code snippets. Scheduling jobs? Build and preview cron expressions with the cron expression builder, or look up the current week with the week number tool.
ISO 8601 is the international standard for representing dates and times as text. Its core format is YYYY-MM-DDThh:mm:ssZ, for example 2026-06-16T09:30:00Z, where the date and time are ordered from the largest unit to the smallest and Z marks UTC. Ordering big-to-small means the strings sort chronologically as plain text, which is why databases, logs, and APIs prefer it.
The ISO week date format is YYYY-Www-D, such as 2026-W25-2. It counts weeks rather than months: week 1 is the week containing the first Thursday of the year, weeks start on Monday, and the final digit is the weekday from 1 (Monday) to 7 (Sunday). Because of this rule, the ISO week-numbering year can differ from the calendar year by a day or two around New Year.
ISO 8601 durations start with P (period). The date part lists years (Y), months (M), and days (D); a T separates the time part, which lists hours (H), minutes (M), and seconds (S). So P1Y2M10DT2H30M is one year, two months, ten days, two hours, and thirty minutes. The M before T is months and the M after T is minutes.
The duration between your input and now is an approximation that uses 30-day months and 365-day years, because calendar months and leap years make exact month-and-year durations ambiguous. For exact elapsed time use the seconds or milliseconds figure, which is always precise.