Date Format Converter
Enter a UTC date and time to see the same instant as an ISO string, UTC-readable text, local-readable text, and Unix timestamps.
Enter a date and time to see ISO, UTC, local, and Unix formats.
Next step: Unix Timestamp Converter
When to use this calculator
Use this calculator whenever you need to see one moment expressed in several common date formats at once—ISO 8601 for APIs and logs, readable text for display, or Unix timestamps for systems that store time as a number.
API and log debugging
Convert a readable date into the ISO 8601 format most APIs and log files expect.
Cross-format verification
Check that an ISO string, a Unix timestamp, and a readable date all represent the same instant.
Local vs UTC comparison
See how the same instant reads in your browser's local time zone versus UTC.
Timestamp conversion instead
For timestamp-to-date conversion in both directions with a timestamp as the primary input, use the Unix Timestamp Converter.
Inputs
Date
The calendar date to convert.
Time
The clock time to combine with the date, treated as UTC.
How the calculation works
The ISO string is the standard UTC representation (ending in Z). UTC and local readable strings use the Intl API with full date and time styles. Local output follows your browser's time zone.
Unix timestamps are shown in seconds and milliseconds since 1970-01-01 UTC. For timestamp ↔ date conversion in both directions, use the Unix Timestamp Converter.
Worked example
Date: 1 January 2025. Time: 12:00 (noon UTC).
ISO string: 2025-01-01T12:00:00.000Z.
UTC readable: Wednesday, January 1, 2025 at 12:00:00 PM UTC.
Unix timestamp: 1735732800 seconds (1735732800000 milliseconds) since 1 January 1970 UTC.
Local readable text depends on your browser's time zone—for a browser set to US Eastern Time, the same instant reads as Wednesday, January 1, 2025 at 7:00:00 AM EST.
Edge cases
Local time zone varies by visitor
The local-readable output is computed from the browser's own time zone setting, so the same input date and time will show different local text for visitors in different regions—the ISO and UTC outputs stay identical for everyone.
Daylight saving time transitions
A local-readable conversion near a daylight saving time change reflects whichever offset was in effect for that specific date, which can differ from the offset in effect today.
Midnight boundary
A time of 00:00 UTC represents the very start of the selected calendar date—useful as a full-day boundary when converting a date-only value.
Related Date & Business Days Calculators
The Business Days vs Calendar Days Guide explains when weekends and holidays count and which day type applies to deadlines, invoices, and contracts.
The How Business Days Are Calculated Guide and Business Days Between Dates Guide cover the counting rules behind every business-day tool on this site.
The Business Days Calculator and Working Days Calculator count weekdays between two known dates, excluding weekends and optional US federal holidays.
The Add Business Days To Date, Subtract Business Days From Date, and Business Day Offset calculators move a single date forward or backward by a business-day count.
The Business Days Until Date Calculator counts business days remaining from today or a custom date to a target deadline.
The Days Between Dates Calculator counts every calendar day between two dates, including weekends—use it instead of the business-day tools when weekends should count.
The Date Range Calculator and Date Duration Calculator break a range into calendar-day totals or a years/months/days breakdown, with inclusive or exclusive boundary options.
The Add or Subtract Days Calculator shifts a single date forward or backward by days, weeks, or months.
The Age Calculator applies the same calendar breakdown used by Date Duration to a birth date, expressed as years, months, and days.
The Hours Between Dates and Date Difference calculators measure elapsed time between two date-times down to hours, minutes, and seconds.
The Date Format Converter, Unix Timestamp Converter, and Timezone Converter handle format and zone conversion for a single instant rather than a span between two dates.
FAQ
- What is the ISO 8601 format?
- A standardized text representation of a date and time, such as 2025-01-01T12:00:00.000Z. The trailing Z indicates the time is in UTC. It's widely used in APIs, databases, and log files.
- Why does the local time differ from UTC?
- Local readable text is formatted using your browser's time zone setting, which is offset from UTC by a fixed or daylight-saving-adjusted amount depending on your region.
- What's the difference between the seconds and milliseconds timestamp?
- Both represent the same instant—milliseconds is simply the seconds value multiplied by 1000, offering sub-second precision that most systems don't need for date-only values.
- How is this different from the Unix Timestamp Converter?
- This calculator starts from a date and time and shows several output formats at once. The Unix Timestamp Converter is bidirectional—enter either a timestamp or a date, and it converts to the other.
Related Guides
- Date Format GuideLearn the most common date format standards—ISO 8601, US, UK, Unix timestamps, and locale-specific patterns—and how to convert between them with DateToolsHQ.
- Unix Timestamp GuideLearn what Unix timestamps are, how they work, why they are timezone-independent, and how to convert between timestamps and human-readable dates with DateToolsHQ.
- Timezone GuideLearn how timezones work, what UTC offsets and daylight saving time mean, and how to convert times between timezones using DateToolsHQ.
- Date Calculation ReferenceA practical reference for calendar days, business days, date ranges, and which DateToolsHQ calculator fits each question.
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