Unix Timestamps Explained: Common Developer Mistakes and How to Avoid Them

Unix timestamps count the seconds (or milliseconds) elapsed since January 1, 1970 at 00:00:00 UTC, a reference point known as the Unix epoch. One of the most frequent developer errors involves confusing second-based timestamps (10 digits) with millisecond-based ones (13 digits), which can cause dates to display incorrectly by decades. JavaScript's Date API expects milliseconds, so passing a seconds-based timestamp directly without multiplying by 1000 will produce a wrong date near January 1970. Importantly, a Unix timestamp carries no time zone information — it represents a single universal instant, and only its human-readable formatting changes across time zones. Developers are advised to always store timestamps in UTC, avoid manual time-zone offsets, and account for daylight saving time when converting timestamps to local representations.