Free browser tool

Timestamp Converter

Convert Unix timestamps to readable UTC and local dates, or convert ISO and local date strings back to Unix time.

Updated 2026-05-12

Unix timestamp Timestamp unit

Example presets

Date, local time, or ISO string

Copyable output

Field notes

Timestamp conversion notes for logs, APIs, and scheduled jobs

Timestamps are easy to misread because the number alone does not say whether it is seconds or milliseconds, and the displayed date changes when a system uses local time instead of UTC. This tool keeps both forms visible so debugging is less error-prone.

Seconds versus milliseconds

Unix seconds are usually 10 digits for current dates. Unix milliseconds are usually 13 digits. Mixing them up is one of the most common causes of dates that land in 1970 or far in the future.

When you copy a timestamp from JavaScript, it is often milliseconds from Date.now(). When you copy a timestamp from many APIs, databases, or logs, it may be seconds. Always check the expected unit before converting.

10 digit current timestamp: usually seconds.
13 digit current timestamp: usually milliseconds.
ISO strings are readable, but still need a timezone assumption.
UTC is safer for logs, cross-region systems, and scheduled jobs.

Node.js seconds to ISO js

const seconds = 1717243200;
const date = new Date(seconds * 1000);

console.log(date.toISOString());
console.log(Math.floor(date.getTime() / 1000));

Timezone traps

A timestamp represents a moment. A local date string represents how that moment looks in a timezone. Two people can convert the same timestamp and see different local clock times while both results are correct.

Use UTC for storage and comparison. Use local time only when the user needs a calendar or clock display. If a bug report includes a local time, add the timezone name or UTC offset.

Java Instant conversion java

import java.time.Instant;
import java.time.ZoneId;
import java.time.format.DateTimeFormatter;

long seconds = 1717243200L;
Instant instant = Instant.ofEpochSecond(seconds);
String utc = DateTimeFormatter.ISO_INSTANT.format(instant);
String local = instant.atZone(ZoneId.systemDefault()).toString();

API and database review

Before blaming an API for a wrong date, verify the unit, timezone, and serialization path. A backend may store seconds, a frontend may multiply by 1000, and a database may display the value in a session timezone.

For scheduled jobs, compare the intended local time with the UTC instant that the scheduler will actually run. Daylight saving time and server timezone defaults are frequent sources of off-by-one-hour behavior.

Common mistakes

Do not strip the Z from an ISO string unless you understand the timezone change. Do not compare formatted date strings when a numeric timestamp or ISO instant is available. Do not assume a date picker returns UTC unless the documentation says so.

How to use this tool

Paste or type your input into the tool.
Choose the action or option that matches your task.
Review the output before copying it into another app.

Notes

Convert seconds, milliseconds, current time, and ISO date strings with validation, timezone notes, copyable output, and clear UTC/local summaries.

Inputs are processed in the browser for this static MVP. Avoid pasting secrets into any online tool unless you understand the environment.

FAQ

What is the difference between seconds and milliseconds?

Unix seconds count whole seconds since 1970-01-01 UTC. Milliseconds are one thousand times larger and usually appear as 13 digits for current dates.

Why can local time differ from UTC?

Local time uses the timezone configured in your browser. UTC is the fixed reference time, so it is safer for logs, APIs, and cross-region debugging.

How does auto detect choose seconds or milliseconds?

Auto detect treats very large values as milliseconds and smaller values as seconds. Choose the unit manually when old dates or unusual test values are ambiguous.

What date format is safest to paste?

An ISO string with a timezone, such as 2024-05-12T16:00:00.000Z, is safest because the exact moment is clear across browsers and locales.

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