What a Unix timestamp is
A Unix timestamp counts the seconds since 1970-01-01 00:00:00 UTC. That moment is called the epoch. The number has no time zone. It is the same instant everywhere on Earth. When you see 1750000000, you are looking at a single point in time, not a clock reading in a city.
Leap seconds are ignored. Every day is treated as exactly 86,400 seconds. This keeps the math simple and predictable. The trade-off is that Unix time drifts about one second behind UTC over a few years, then gets corrected by other systems.
JavaScript uses milliseconds instead of seconds. That is why you sometimes see 13-digit numbers. A 10-digit number is seconds. A 13-digit number is milliseconds. This converter reads both and tells you which one it found.
How to convert in both directions
Paste a timestamp into the input and the page shows the date in UTC and in your local time zone. You can also pick a date and time, and the page gives you the matching epoch value. The current timestamp updates live at the top of the page.
Here is a worked example. Take the timestamp 1750000000. Divide by 86,400 to get the number of whole days since the epoch. That is 20,254 days, with 54,400 seconds left over, which is 15 hours, 6 minutes and 40 seconds. So 1750000000 is 2025-06-15 15:06:40 UTC (a Sunday). In New York, which is UTC-4 in June, that is 11:06:40 local time.
To go the other way, start with a date. Count the days from 1970-01-01 to your date. Multiply by 86,400. Add the seconds since midnight UTC. The result is the timestamp. The converter does this for you, including the leap years.
Why milliseconds show up
JavaScript's Date object stores time in milliseconds. When you call Date.now(), you get a 13-digit number. Many APIs and databases also use milliseconds. If you paste a 13-digit number into a seconds-only converter, you get a date far in the future. This tool checks the digit count and picks the right unit.
Some systems use microseconds or nanoseconds. Those are 16 or 19 digits. This converter does not handle them. If you have a number that long, divide by 1,000 or 1,000,000 first to get milliseconds.
The 2038 problem
Many older systems store Unix time in a signed 32-bit integer. That counter runs out on 2038-01-19. After that moment, it wraps to a negative number and can show dates in 1901. Modern 64-bit systems do not have this limit. If you work with embedded devices or old databases, check how they store time.
Common uses
- Reading log files where each line starts with a timestamp.
- Checking when a token or license expires.
- Converting an API response into a date you can read.
- Setting a date in a database that expects epoch seconds.
- Comparing two events that happened in different time zones.
If you need to add or subtract time from a date, try the date calculator. For time zone conversions, use the time zone converter. To see how we handle leap years and day counts, read how we calculate.