Question 1

What is a Unix timestamp?

Accepted Answer

A Unix timestamp is the number of seconds (or milliseconds) elapsed since 00:00:00 UTC on 1 January 1970, also known as the Unix epoch. Leap seconds are NOT counted — every day has exactly 86,400 seconds in this scheme. This makes Unix time unambiguous and timezone-independent, which is why it's the default time format in databases, APIs, and log files.

Question 2

How does the seconds vs milliseconds detection work?

Accepted Answer

We classify any number with 13 or more digits (≥ 10¹²) as milliseconds, and anything smaller as seconds. This works because 10¹² seconds is the year 33,658, well past the year-2100 cap, while 10¹² milliseconds is the year 2001 — comfortably inside the millisecond range. The detected unit is shown in the result for transparency.

Question 3

Why does the date input show local time but the result lists UTC?

Accepted Answer

The `<input type="datetime-local">` field accepts wall-clock time in your local zone — that's how the browser presents it. When you type a date there, we convert it to a Unix timestamp using your local zone, so "2024-06-15 09:00" becomes a different epoch second in New York vs Tokyo. The result panel lists both the UTC interpretation (canonical) and your local interpretation so you can see exactly what the timestamp represents.

Question 4

What is the largest timestamp accepted?

Accepted Answer

4,102,444,800 seconds — that's 1 January 2100 UTC. Beyond that, the tool returns an error. This is a deliberate guardrail against typos: a 16-digit number entered as seconds would give a year-100k+ result that pretends to be valid. If you genuinely need post-2100 dates, append three zeros and enter as milliseconds.

Unix Timestamp Converter

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