This is a practical reference for use valid machine-readable dates and times. Keep it nearby when you are writing a page, but do not worry about memorizing every entry at once.
What this reference covers
Use valid machine-readable dates and times. The entries below summarize the most useful choices and what each one means.
| Value or item | What it means |
|---|---|
YYYY-MM-DD | Calendar date |
HH:mm | 24-hour time |
YYYY-MM | Month |
YYYY-Www | ISO week |
YYYY-MM-DDTHH:mm | Local date and time |
Z | UTC designator with suitable ISO date-time formats |
±HH:mm | Time-zone offset |
duration | Specific ISO-8601 duration forms in contexts that accept them |
See it in HTML
A small example shows how one of these ideas appears in a normal page:
<time datetime="2026-11-10">November 10, 2026</time>
<time datetime="2026-11-10T14:30">2:30 PM on November 10</time>How to use the reference
Begin by identifying what the page is trying to achieve. Then choose the entry that describes that job, instead of choosing a setting merely because it looks familiar.
Read the code from the outer element inward. Pay attention to attribute names, tag nesting, and any links between elements through IDs. A browser may accept some incorrect markup, but accepting it is not the same as using it correctly.
A useful check before publishing
Try changing one choice in the example while keeping the rest of the page the same. Inspect the result in your browser. For compatibility-sensitive features, test another browser; for accessibility-sensitive features, use keyboard navigation and an accessibility inspector.
Some entries describe browser hints rather than guarantees. User input still needs server-side validation, and event-based behavior needs JavaScript even if the HTML describes the control.
Common Beginner Mistakes
- Treating every item in a reference list as interchangeable instead of choosing the one that matches the job.
- Copying reference markup without checking the element’s surrounding context or required attributes.
- Assuming one successful browser test proves the markup is accessible or universally supported.
Key Takeaways
- Use valid machine-readable dates and times.
- Pick a setting for its meaning, then test the smallest working example.
- HTML references are most useful when combined with validation, browser inspection, and accessibility testing.