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Unix Timestamp Converter

Turn a Unix timestamp in seconds or milliseconds into a readable UTC date and time, or a date back into a timestamp, with an optional local time zone.

Level: Grades 5–6

  • Common Core standard 5.MD.A.1Convert among different-sized standard measurement units within a given measurement system (e.g., convert 5 cm to 0.05 m), and use these conversions in solving multi-step, real world problems.
Printable worksheet

Unix Timestamp Converter

Inputs
Convert

Seconds since 00:00:00 UTC on January 1, 1970. Negative values are earlier. A 13-digit value is usually milliseconds.

This only changes the extra local-time line. The conversion itself is always in UTC.

Result

Calculating…

Test yourself

20 quick questions built from this calculator's formula: work out results, predict what happens when an input changes, and work backward from an answer. Every answer comes with the working.

What this calculator does

Find out what date and time a computer timestamp stands for, or get the timestamp for any date. Computers rarely store a moment as a date and a clock time. Instead, most systems count the seconds since midnight on January 1, 1970, in UTC. UTC (Coordinated Universal Time) is the world's reference clock, the same everywhere. That starting moment is called the Unix epoch.

The count is called a Unix timestamp, or epoch time. Operating systems, databases, programming languages and log files all use it. It's short and can only mean one moment. But a number like 1800000000 tells a person very little until you convert it.

This converter works both ways. Paste a timestamp in seconds or milliseconds to get the UTC date and time. You also get its ISO 8601 form, a standard way of writing dates. If you like, you'll see the local clock time in a time zone you pick. Or enter a UTC date and time to get the timestamp a program would store for it.

Where it's used

Why this math matters outside the classroom:

  • Reading server logs. Developers convert a log entry stamped 1800000000 to 08:00:00 UTC on January 15, 2027.
  • Database records. Analysts turn a created-at value in milliseconds into a readable date by dividing it by 1,000 first.
  • Scheduling jobs. Programmers store a reminder for noon UTC on October 18, 2026 as the timestamp 1792324800.
  • Unit conversion practice. Students convert 28,800 seconds to 480 minutes and then to 8 hours using 60 and 3,600 as factors.
  • Year 2038 planning. Engineers check that dates after 2,147,483,647 seconds, January 19, 2038, still fit in their data types.

Grade level and standards: Grades 5–6; Common Core State Standards for Mathematics 5.MD.A.1. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.

How to use it

  1. Choose "Timestamp to date" or "Date to timestamp".
  2. For a timestamp, paste the number and choose seconds or milliseconds. For present-day dates, ten digits is usually seconds and thirteen digits is usually milliseconds.
  3. For a date, enter the date, the time and the seconds in UTC.
  4. If you like, pick a time zone to see the same moment on local clocks. You'll also see that zone's offset from UTC on that date.

What the inputs mean

Unix timestamp
Negative values are moments before 1970: −86,400 is midnight UTC on December 31, 1969. Fractions of a second are kept to the millisecond.
Time (UTC, 24-hour)
Enter the time in UTC. To convert a local time, first subtract the zone's offset from UTC (or use the time zone converter).
Also show in time zone
The local line uses your device's built-in list of time-zone rules. So daylight saving time is applied correctly for that exact moment. The timestamp itself never depends on a time zone.

Formula and method

days = ⌊timestamp ÷ 86,400⌋
time of day (s) = timestamp − days × 86,400
date = January 1, 1970 + days
timestamp = days since 1970-01-01 × 86,400 + hours × 3,600 + minutes × 60 + seconds
milliseconds = seconds × 1,000

Unix time treats every day as exactly 86,400 seconds (24 × 60 × 60). The brackets ⌊ ⌋ mean "round down to a whole number". So dividing by 86,400 and rounding down gives the whole days since the epoch. What's left over is the time of day in UTC.

Rounding down, rather than toward zero, makes negative timestamps work. For example, −1 is 23:59:59 on the day before the epoch, not 00:00:01.

Counting the whole days forward from January 1, 1970 gives the date. The count uses our everyday (Gregorian) calendar, with its leap years. Going the other way, the calculator multiplies the days back by 86,400 and adds the clock time in seconds.

Unix time doesn't count leap seconds (the odd extra second sometimes added to keep clocks in step with the Earth). That's why every day can be treated as exactly 86,400 seconds. The calculator follows the same rule.

For the optional time zone, the calculator asks the built-in time-zone rules for the local date, time and offset at that moment.

Worked example

A log line shows the timestamp 1800000000. When was that?

  1. Whole days: 1,800,000,000 ÷ 86,400 = 20,833.33…, which rounds down to 20,833 days.
  2. Seconds left over: 1,800,000,000 − 20,833 × 86,400 = 28,800 s.
  3. 28,800 s = 8 h 0 min 0 s, so the UTC time is 08:00:00.
  4. 20,833 days after January 1, 1970 is Friday, January 15, 2027.
  5. In Chicago (UTC−6 in January) the same moment is 2:00:00 AM.

Result: Unix time 1800000000 is Fri, Jan 15, 2027 08:00:00 UTC, written 2027-01-15T08:00:00Z.

Understanding the result

The UTC result is the same for everyone. Local times differ by zone. In zones with daylight saving time, the offset also depends on the date.

ISO 8601 text, such as 2027-01-15T08:00:00Z, is the safest way to write the time for both people and programs. The Z at the end means UTC.

Did your date land in January 1970 when you expected a recent one? Then the value was probably in seconds, but you chose milliseconds. If it lands tens of thousands of years ahead, it's the other way around.

Assumptions and limitations

  • Unix time without leap seconds: every day is 86,400 seconds.
  • Dates use the everyday (Gregorian) calendar in UTC, from the year 1 to 9999.
  • It doesn't convert leap seconds or other time scales (such as GPS or TAI time).
  • Very old local times follow whatever historical rules the time-zone list holds. Before standard time zones existed, that may be local mean time (time set by the sun in each town).
  • Divide microsecond and nanosecond timestamps down to milliseconds first.

Frequently asked questions

What is the Unix epoch?

It's the starting point of Unix time: 00:00:00 UTC on Thursday, January 1, 1970. A timestamp is the number of seconds since then, so the epoch itself is timestamp 0.

How do I tell seconds from milliseconds?

For dates between 2001 and 2286, a seconds timestamp has 10 digits and a milliseconds timestamp has 13. Many programming languages and browsers use milliseconds. Most databases and command-line tools use seconds.

What happens in 2038?

Some systems store Unix time as a signed 32-bit number. Those can count only up to 2,147,483,647, which is 03:14:07 UTC on January 19, 2038. One second later, the number overflows (runs out of room and wraps around). Systems using 64-bit numbers aren't affected.

Does a Unix timestamp depend on my time zone?

No. It counts seconds from a fixed moment in UTC, so the same moment has the same timestamp everywhere. Only the way the moment is shown changes with the time zone.

How this calculator is checked

Method: POSIX Unix time definition (86,400 seconds per day from 1970-01-01T00:00:00Z, no leap seconds); IANA time-zone data via the Intl API for the optional local display. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

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