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HomeTimestamp ConverterISO 8601 validator

ISO 8601 · RFC 3339

ISO 8601 date
validator and converter

Check whether a date string clearly identifies an instant. Validate Z or a numeric UTC offset, preserve up to nine fractional-second digits and compare UTC, Korea time and exact Unix values.

An explicit offset prevents the same clock reading from being interpreted in different regions.

Validate and convert an ISO date string

Include Z or a ±HH:mm offset. Up to nine fractional-second digits are retained.

Validation result—
Normalized UTC form
—
Entered UTC offset—
Coordinated Universal Time—
Korea Standard Time—
Your device time—
Unix seconds
—
Unix milliseconds
—
Unix microseconds
—
Unix nanoseconds
—

Your date string is checked only on this page. It is not sent or stored.

Anatomy of an ISO 8601 date-time

A complete internet timestamp combines a calendar date, clock time and explicit relationship to UTC.

PartExampleMeaning
Date2024-01-01Year, month and day
SeparatorTSeparates the date and clock time
Time09:00:00Hour, minute and second
Fraction.123456789Optional subsecond precision
Offset+09:00The entered clock is nine hours ahead of UTC
Equivalent instants2024-01-01T00:00:00Z and 2024-01-01T09:00:00+09:00 look different but identify exactly the same moment.

What this validator checks

The input is validated strictly so an impossible or ambiguous date is not silently adjusted.

Z

Required offset

Use Z for UTC or a numeric offset such as -05:00 or +09:00.

29

Real calendar dates

Month lengths and Gregorian leap years are checked. Invalid dates such as February 30 are rejected.

.9

Exact fractional digits

One through nine fractional digits are preserved rather than rounded through a floating-point number.

Offset is not a named time zone. -05:00 describes a numeric difference from UTC but does not identify New York or its daylight-saving rules. Use the relevant IANA zone for historical regional schedules.

Valid and invalid examples

Compare the syntax before using a date in an API, log or shared schedule.

InputStatusReason
2024-01-01T00:00:00ZValidUTC is explicit
2024-01-01T09:00:00+09:00ValidNumeric offset is explicit
2024-01-01T00:00:00.123456789ZValidNine fractional digits
2024-01-01 00:00:00RejectedNo T separator or offset
2024-02-30T00:00:00ZRejectedImpossible calendar date
2016-12-31T23:59:60ZRejectedLeap second is outside this Unix conversion model

The internet date-time profile is defined by RFC 3339. Regional rules are maintained in the IANA Time Zone Database.

ISO 8601 questions

Common questions about offsets, fractions and Unix conversion.

What does Z mean at the end of an ISO date?

Z marks a UTC offset of zero. 2024-01-01T00:00:00Z identifies the same instant as 2024-01-01T09:00:00+09:00.

Is a time-zone offset required?

This validator requires Z or a numeric offset so the string identifies one unambiguous instant rather than only a local clock reading.

How many fractional-second digits are supported?

Up to nine digits are preserved, covering millisecond, microsecond and nanosecond notation.

Does this validator accept leap-second notation such as 23:59:60?

No. It rejects second 60 because conventional Unix time does not represent a leap second as an ordinary additional second.

Move between a validated string, Unix units and regional date displays.

Calendar input

Date → Unix time

Choose UTC, KST or device-local time from a calendar field.

Calculate a timestamp →Numeric input

Timestamp → date

Convert seconds through nanoseconds to an exact ISO date.

Show a date →Time-zone comparison

UTC ↔ KST

Compare both clock displays and check day rollover.

Convert UTC and KST →