Developer guides
Practical guides for developers — Unix timestamps, time zones, date formats, encoding and the everyday data-handling mistakes that cause subtle bugs.
Articles in Developer
Unix Timestamps Explained: Seconds, Milliseconds, Time Zones and Common Mistakes
Seconds or milliseconds, UTC or local time — how Unix timestamps really work and the mistakes that cause date bugs.
Unix Timestamp 0: The Unix Epoch and Why Dates Show 1970
Timestamp 0 is where Unix time begins. It is also the date you see when a null, a zero or a unit mix-up slips into your code.
Unix Timestamp 1000000000: The 2001 Unix Billennium
One billion seconds after the epoch, Unix time gained its tenth digit. Here is what 1000000000 means and the bugs that digit change exposed.
Unix Timestamp 1234567890: Friday the 13th, February 2009
The most memorable Unix timestamp ever: 1234567890 landed on Friday the 13th in UTC and on Valentine's Day in much of the world.
Unix Time Milestones: 1500000000, 1600000000, 1700000000 and Beyond
Every hundred million seconds, Unix time rolls over another round number. Here are the dates for 1.5, 1.6 and 1.7 billion, and what comes next.
Unix Timestamp 2000000000: 18 May 2033 and the Road to 2038
Two billion seconds after the epoch is May 2033, less than five years before the 32-bit limit. For code that calculates future dates, 2038 is already here.
Unix Timestamp 2147483647 and the Year 2038 Problem Explained
At 03:14:07 UTC on 19 January 2038, a signed 32-bit Unix clock runs out. What happens next, what is affected, and how to find the bug before it finds you.
Unix Timestamp 4294967295 and the Year 2106 Problem
Switch a 32-bit Unix clock from signed to unsigned and it lasts until 2106. Here is what 4294967295 means, and why it keeps appearing as a bogus date.
Unix Timestamp -2147483648: The 1901 Limit and Negative Timestamps
The earliest date a signed 32-bit Unix clock can reach is 13 December 1901. It is also where 2038 overflows land, and a good test of negative time.
About this section
Many hard-to-find bugs come from data that looks correct but is interpreted the wrong way. A timestamp might be in seconds when the code expects milliseconds, a date string might have no time zone, or an encoded value might be decoded with the wrong assumptions.
These guides explain how common data formats work in practice. Each one shows what the value actually represents, which mistakes developers make most often, and how to debug the result when it does not match what you expected.
To check values while you read, use the Timestamp Converter, JSON Formatter, JWT Decoder and Cron Expression Generator.
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