Log files, databases, APIs and spreadsheets exported from web apps often record time as a single large number such as 1800000000. That is Unix time: a count of seconds since the start of 1970 in Coordinated Universal Time. This converter turns those numbers into readable dates and turns dates back into timestamps, in seconds and milliseconds, with ISO 8601 and RFC 2822 formats ready to copy.
How to use the Unix timestamp converter
- Choose Timestamp → date or Date → timestamp.
- For a timestamp, paste the number. Leave the unit on Detect automatically, or choose seconds, milliseconds, microseconds or nanoseconds.
- For a date, pick the date and time.
- Choose the time zone (UTC offset) the date should be shown in, or interpreted in.
- Read the result on the tape. Show the work splits the seconds into days and hours.
Unix time formulas
To decode a timestamp, divide by 86,400: the whole part is the number of days since the epoch and the remainder is the time of day in seconds.
Worked example
Timestamp → date. Take 1,800,000,000 seconds.
- 1,800,000,000 ÷ 86,400 = 20,833 days with 28,800 seconds left over.
- 20,833 days after January 1, 1970 is January 15, 2027.
- 28,800 seconds = 8 hours, so the moment is 2027-01-15T08:00:00Z, a Friday, at 8:00 AM UTC.
- In US Eastern standard time (UTC−05:00) that is 3:00 AM the same day.
Date → timestamp. Noon on July 4, 2026, US Eastern daylight time (UTC−04:00), is 16:00 UTC. That is 20,638 days and 57,600 seconds after the epoch: 20,638 × 86,400 + 57,600 = 1,783,180,800.
Timestamp landmarks
| Timestamp (s) | Date and time (UTC) | Note |
|---|---|---|
| 0 | 1970-01-01 00:00:00 | The Unix epoch |
| 1,000,000,000 | 2001-09-09 01:46:40 | First 10-digit timestamp |
| 1,700,000,000 | 2023-11-14 22:13:20 | |
| 2,000,000,000 | 2033-05-18 03:33:20 | |
| 2,147,483,647 | 2038-01-19 03:14:07 | Signed 32-bit limit |
| −86,400 | 1969-12-31 00:00:00 | Negative values are before 1970 |
Working with timestamps
Seconds versus milliseconds
Unix tools, PHP and Python’s time.time() use seconds; JavaScript’s Date.now() and Java’s System.currentTimeMillis() use milliseconds. Mixing them up produces absurd dates: reading the millisecond value 1,800,000,000,000 as seconds lands in the year 59,009, while reading the seconds value 1,800,000,000 as milliseconds lands on January 21, 1970. If a converted date looks wildly wrong, check the unit first.
Store UTC, display local
Timestamps carry no time zone, which is their strength. Store and compare them as-is, and convert to a local offset only when showing them to people. The time zone converter handles daylight saving rules for named cities.
ISO 8601 for humans and machines
The ISO 8601 format, such as 2027-01-15T08:00:00Z, sorts correctly as text and is unambiguous across countries. The “Z” suffix means UTC (often read “Zulu”); other offsets are written like −05:00.
To count the days between two calendar dates instead, use the date difference calculator.
Frequently asked questions
What is a Unix timestamp?
The number of seconds that have elapsed since 00:00:00 UTC on January 1, 1970, a moment called the Unix epoch. It is time-zone independent, which is why servers, databases and APIs use it to record when things happen.
How can I tell if a timestamp is in seconds or milliseconds?
Count the digits. Present-day timestamps have 10 digits in seconds, 13 in milliseconds, 16 in microseconds and 19 in nanoseconds. The automatic setting uses those lengths to choose the unit.
What is the Year 2038 problem?
Systems that store Unix time as a signed 32-bit integer can count only to 2,147,483,647, which is 03:14:07 UTC on January 19, 2038. One second later the value overflows. Modern systems use 64-bit time, which lasts billions of years.
Does Unix time include leap seconds?
No. Unix time treats every day as exactly 86,400 seconds and ignores leap seconds, so it is not a perfect count of elapsed SI seconds. For everyday dates the difference does not matter.
Why does the calculator ask for a UTC offset instead of a city?
A fixed offset gives the same answer every time, with no dependence on a device's time-zone database. Remember that daylight saving time changes the offset: US Eastern time is UTC−05:00 in winter and UTC−04:00 in summer.