What a Unix timestamp actually is.

A Unix timestamp is the number of seconds that have passed since 00:00:00 Coordinated Universal Time (UTC) on 1 January 1970. That starting instant is called the Unix epoch, and every timestamp is measured forward from it. As you read this, the current value is somewhere north of 1.7 billion.

The reason computers agreed on one arbitrary date is efficiency. A single integer is far easier to store, compare, and do math on than a string like "June 24, 2026, 3:14 PM in Central European Summer Time." Sorting events, measuring how long something took, or checking whether one thing happened before another all reduce to comparing two whole numbers.

Because the count is anchored to UTC, a Unix timestamp has no time zone baked in. The same number, 1750000000, is one instant in time everywhere on Earth — it just displays as a different wall-clock time in Tokyo than in New York. Time zones are applied only when the number is turned back into a human-readable date.

The classic Unix timestamp is measured in seconds, but a lot of modern software — JavaScript in particular — measures in milliseconds, which is 1000 times larger. Mixing the two is the single most common timestamp bug, and it produces dates that are either in 1970 or roughly 50,000 years in the future.

The quickest way to tell them apart is digit count. A seconds timestamp for any recent date has 10 digits (1750000000). The millisecond version of the same instant has 13 digits (1750000000000). If a value looks 1000x too big, it is almost certainly milliseconds — divide by 1000 to get seconds. If a library expects milliseconds and you hand it seconds, multiply by 1000.

A few systems go finer still: microseconds (16 digits) and nanoseconds (19 digits) show up in high-resolution logging and databases. The rule is the same — each step is another factor of 1000. When in doubt, paste the number into a converter and see whether the resulting date is anywhere near today.

The epoch was chosen in the early 1970s by the engineers building Unix at Bell Labs. It needed to be a recent, round, convenient date, and the start of 1970 fit — it was close enough that the counter would not immediately need huge numbers, and far enough back to cover the file and process times they cared about. Negative timestamps represent moments before 1970, so the scheme handles historical dates too.

One subtlety: Unix time ignores leap seconds. Real UTC occasionally inserts an extra second to stay aligned with the Earth's slightly irregular rotation, but Unix time pretends every day has exactly 86,400 seconds. This keeps the arithmetic simple at the cost of being a fraction of a minute off from strict astronomical time — a tradeoff almost everyone is happy to make.

When you need to line up a timestamp with a Discord event, a cron schedule, or a countdown, it helps to pair the converter with a time-zone tool so you can see the same instant across the regions your audience lives in.