Format Dates to ISO 8601 Standard Format any date/time into ISO 8601 standard format with multiple variants.

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ISO 8601 Formatter

Format any date/time into ISO 8601 standard format with multiple variants.

Enter a Date

Use the date picker or type a date string.

Choose Options

Toggle time inclusion, timezone, and UTC vs local display.

Copy Results

Copy any of the ISO 8601 format variants with one click.

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What Is ISO 8601 Formatter?

The ISO 8601 Formatter converts any date into multiple standard format variants. ISO 8601 is the international standard for representing dates and times, widely used in APIs, databases, file naming, and data interchange. This tool generates the full standard format (with date, time, and timezone), date-only format (YYYY-MM-DD), week number format (YYYY-Wnn), ordinal date format (YYYY-DDD), and the Unix timestamp. You can toggle options for including time, including the timezone offset, and choosing between UTC and local time representation. Each format variant includes a one-click copy button for easy use. The tool accepts both date picker input and free-text date strings.

Why Use ISO 8601 Formatter?

Multiple ISO 8601 variants generated simultaneously
Toggle between UTC and local time
Optional time and timezone inclusion
One-click copy for each format
Accepts both picker and text input for flexibility
Essential for developers and data professionals

Common Use Cases

API Development

Generate properly formatted ISO 8601 timestamps for API requests and responses.

Database Entry

Create standardized date strings for database columns and queries.

File Naming

Generate YYYYMMDD-formatted dates for consistent file naming conventions.

Data Exchange

Ensure dates in CSV/JSON exports follow the international standard.

Documentation

Format dates consistently in technical documentation and specifications.

Technical Guide

The formatter uses JavaScript's Date object combined with manual string construction for precise control over format output. The full ISO 8601 format uses toISOString() which always returns UTC time with the Z suffix. For local time variants, the formatter manually constructs the string using getFullYear(), getMonth(), getDate(), getHours(), getMinutes(), and getSeconds() with zero-padding. The timezone offset is calculated from getTimezoneOffset() and formatted as ±HH:MM. The ISO week number uses the standard algorithm: find the Thursday of the current week, determine its year, and calculate the week number as the ordinal day of that Thursday divided by 7. The ordinal date (day of year) is computed as the difference in days from January 0 of the same year.

Tips & Best Practices

1
Use the YYYY-MM-DD format for most database and API use cases
2
The week number format (YYYY-Wnn) is used in European business contexts
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Toggle UTC for server-side timestamps, local for user-facing displays
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The compact format (YYYYMMDD) is ideal for file naming
5
Remember that ISO 8601 month numbering starts at 01, not 00

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Frequently Asked Questions

Q What is ISO 8601?

ISO 8601 is an international standard for date and time representation. The most common format is YYYY-MM-DD for dates and YYYY-MM-DDThh:mm:ssZ for timestamps.

Q What does the Z mean in ISO dates?

The Z suffix indicates UTC (Coordinated Universal Time), also known as Zulu time. It means the time has no timezone offset.

Q Should I use UTC or local time?

Use UTC for server-side storage and APIs. Use local time for user-facing displays. The tool lets you toggle between both.

Q What is the week number format?

ISO 8601 defines a week numbering system where weeks start on Monday and the first week of the year contains the first Thursday. Format: YYYY-Wnn.

Q What is ordinal date format?

Ordinal date format represents a date as the year followed by the day number within that year (1-365 or 366). Format: YYYY-DDD.

About This Tool

ISO 8601 Formatter is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.