ISO Timestamp with Milliseconds – Convert Fractional Seconds

Local only

Show how fractional milliseconds are preserved even though the primary Unix output is integer seconds.

Multi-row timestamp converter

Compare timestamps and ISO 8601 dates. Inputs without an offset use UTC.

Row 1Date -> Timestamp
1705321845
Milliseconds: 1705321845123Timezone: UTC (Z)ISO: 2024-01-15T12:30:45.123Z

Timestamp precision

What happens to milliseconds when an ISO timestamp becomes Unix time?

ISO 8601 can carry fractional seconds such as .123. VetaTool keeps that precision in the millisecond detail and normalized ISO value while the main Date to Timestamp output is integer Unix seconds. This tool is free to use. No account or payment is required.

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What you can do here

  • Unix seconds and milliseconds conversion
  • ISO 8601 parsing
  • Explicit timezone interpretation
  • Fractional and negative Unix timestamps
  • Browser-local processing

Steps

  1. Paste the ISO timestamp with its fractional seconds intact.
  2. Read the main Unix-seconds output.
  3. Use the Milliseconds detail when the destination needs sub-second precision.

Integer seconds do not mean the milliseconds were lost

The primary Date to Timestamp result uses Math.floor to return whole Unix seconds. The details still expose the exact millisecond count and ISO value with .123 preserved.

ISO milliseconds example

The .123 fraction remains visible in both milliseconds and ISO details.

ISO timestamp

2024-01-15T12:30:45.123Z

Unix seconds

1705321845

Common questions

Frequently asked questions

Why does the seconds result not include .123?

The main output is whole Unix seconds. Use the Milliseconds detail for the exact sub-second instant.

Is the fractional value preserved anywhere?

Yes. The Milliseconds detail is 1705321845123 and the normalized ISO value keeps .123Z.

Recommended next steps

Decimal Unix Timestamp SecondsKeep fractional seconds and inspect the resulting millisecond precision.ISO Date to Unix TimestampConvert an explicit UTC ISO 8601 date into Unix seconds and milliseconds.Unix Timestamp Converter OnlineConvert Unix seconds, milliseconds, ISO 8601 dates, and timezone-aware values locally.

Debugging a specific Timestamp issue? Browse Timestamp troubleshooting.