Timestamp Fractional Seconds Precision – Microseconds to Milliseconds

Local only

Explain how supported ISO input with microsecond-like precision is normalized to milliseconds.

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

Fractional-second normalization

What happens to microsecond digits in a JavaScript timestamp?

The supported ISO parser accepts a fractional-second sequence, but JavaScript Date stores time at millisecond precision. An input ending in .123456Z therefore normalizes to .123Z. 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 high-precision ISO timestamp.
  2. Compare the input fraction with the normalized ISO detail.
  3. Preserve the original source string separately if microseconds or nanoseconds are significant.

JavaScript Date is millisecond based

The converter does not invent sub-millisecond storage. Additional fractional digits beyond milliseconds are discarded by the underlying Date representation.

Six fractional digits example

.123456Z normalizes to .123Z.

ISO timestamp

2024-01-15T12:30:45.123456Z

Normalized ISO detail

2024-01-15T12:30:45.123Z

Common questions

Frequently asked questions

Does the converter round .123456 to .123?

The JavaScript Date result retains millisecond precision; this example normalizes to .123Z.

Can I recover the discarded digits from the Unix output?

No. Keep the original higher-precision source if those digits matter.

Recommended next steps

ISO Timestamp with MillisecondsPreserve fractional milliseconds from an ISO 8601 input while returning Unix seconds.Decimal Unix Timestamp SecondsKeep fractional seconds and inspect the resulting millisecond precision.Unix Timestamp Converter OnlineConvert Unix seconds, milliseconds, ISO 8601 dates, and timezone-aware values locally.

Debugging a specific Timestamp issue? Browse Timestamp troubleshooting.