Why is my date wrong by hours?

Time zone interpretation or ms vs s scaling is the usual culprit.

Strings with Z suffix?

Z means UTC; do not double-apply offsets.

Excel date serial numbers?

Not UNIX epochs—convert with spreadsheet-specific rules.

Timestamp Converter

UNIX epoch ⇄ ISO 8601 ⇄ Local / UTC time

Use UTC

Timezone:

UNIX Timestamp (seconds)

UNIX Timestamp (milliseconds)

ISO 8601

Local Date & Time

UTC Date & Time

Timestamp converter: UNIX time, ISO 8601, and time zones

Developers juggle epoch seconds, milliseconds, RFC3339 strings, and local wall times when debugging logs, JWT exp claims, and database fields. A timestamp converter reduces off-by-one thousand errors and clarifies UTC vs local.

Always label whether a value is seconds or milliseconds—libraries differ.

Practical tips

Store UTC in databases; render local in UI.
Account for DST when interpreting “next day” in local time.
Use ISO strings in APIs for human readability.
Beware leap seconds in ultra-precise science contexts.

Common questions

Why is my date wrong by hours?: Time zone interpretation or ms vs s scaling is the usual culprit.
Strings with Z suffix?: Z means UTC; do not double-apply offsets.
Excel date serial numbers?: Not UNIX epochs—convert with spreadsheet-specific rules.

Related tools on Toolfex

Toolfex provides free online utilities for individuals and teams. Use these guides alongside each tool’s on-page controls. For privacy and data handling, see our Privacy Policy.