What Is a Unix Timestamp and How to Convert It Online

What Is a Unix Timestamp and How to Convert It Online

If you've ever inspected an API response, a database record, or a JWT token, you've probably seen a date represented as a strange number like 1735689600 instead of a readable date. That number is a Unix timestamp — and once you know how to convert it, it stops being mysterious.

This guide explains what a Unix timestamp actually is, why systems use it, and how to convert it to and from a human-readable date in seconds.

What Is a Unix Timestamp?

A Unix timestamp (also called epoch time) is the number of seconds that have elapsed since January 1, 1970, 00:00:00 UTC — a moment known as the Unix epoch. Instead of storing a date as "July 1, 2026," a computer stores it as a single integer counting seconds since that reference point.

This has real advantages for software:

• •It's timezone-independent — the same number represents the same instant everywhere in the world
• •It's easy to compare — checking if one timestamp is before another is just integer comparison
• •It's compact — a date and time fits in a single number instead of a formatted string

Most backend systems, databases, and APIs use Unix timestamps internally, even if they display formatted dates to end users.

Seconds vs. Milliseconds

This is the single most common source of confusion. There are two common variants:

• •Unix timestamp in seconds — the traditional format, used by most APIs, Linux systems, and JWTs (10 digits for dates in the current era)
• •Unix timestamp in milliseconds — used by JavaScript's Date.now() and many web APIs (13 digits for dates in the current era)

If you paste a 13-digit number into a converter expecting seconds, you'll get a date far in the future or a parsing error. A good converter lets you pick the unit or detects it automatically based on digit count.

Example Conversions

Notice how the same instant in seconds and milliseconds looks different — the millisecond version is just the seconds value multiplied by 1000.

Why Developers Convert Timestamps Constantly

• •Debugging API responses — most JSON APIs return created_at, updated_at, or expires_at fields as raw timestamps
• •Reading JWT claims — JSON Web Tokens use exp (expiration) and iat (issued at) claims, both stored as Unix timestamps in seconds. If you're decoding a JWT with the JWT Decoder, you'll frequently need to convert the exp value into a real date to check if a token has expired
• •Database inspection — many databases store timestamps as integers for indexing efficiency
• •Log file analysis — server logs often timestamp entries in epoch time for consistent sorting
• •Cron and scheduling — some scheduling systems accept or return epoch time for the next run

Converting a Timestamp to a Date, and Back

Using the ToolzGo Unix Timestamp Converter takes a few seconds either direction:

Timestamp to date:

• •Go to toolzgo.com/tools/datetime-tools/unix-timestamp-converter
• •Paste your timestamp into the input field
• •Select whether it's in seconds or milliseconds
• •Read the converted date in both UTC and your local timezone

Date to timestamp:

• •Pick a date and time using the date/time picker
• •Instantly see the equivalent timestamp in both seconds and milliseconds
• •Copy whichever format your API or code needs

The tool also shows a live "current timestamp" reference, which is handy when you need to quickly check what "now" looks like in epoch time.

Timestamps and Timezones

A Unix timestamp itself has no timezone — it represents a single, unambiguous instant in time. The timezone only matters when you convert that instant into a human-readable date, since the same timestamp displays as a different local time depending on where you are. If you need to convert a converted date into a specific timezone for a meeting or event, pair the timestamp converter with the Timezone Converter.

Frequently Asked Questions

Q: Why does my timestamp show a date in 1970?

A: This usually means the timestamp was in seconds but was interpreted as milliseconds, or vice versa. Double-check the unit toggle in the converter.

Q: Is Unix time affected by daylight saving time?

A: No. The raw timestamp is always in UTC and unaffected by DST. Only the human-readable local time you convert it to will shift with DST rules.

Q: What happens when Unix time runs out in 2038?

A: Systems using a signed 32-bit integer for timestamps will overflow on January 19, 2038 — known as the "Year 2038 problem." Most modern systems now use 64-bit integers, which push this limit billions of years into the future.

Q: Can I use this to convert a timestamp from a JWT token?

A: Yes. Copy the exp or iat value from a decoded JWT payload and paste it into the timestamp converter (in seconds) to see the exact expiration or issue date.

Unix timestamps look intimidating until you know the trick: they're just a count of seconds since 1970. Bookmark the ToolzGo Unix Timestamp Converter for the next time you need to make sense of one.

Convert Unix timestamps to dates and back, in seconds or milliseconds.