Unix Timestamp Code Examples

Getting the current epoch, converting a timestamp to a date, and converting a date back — in 21 languages, with the pitfalls each one has.

• Python

  Native unit: float seconds

• JavaScript

  Native unit: integer milliseconds

• PHP

  Native unit: integer seconds

• Java

  Native unit: integer milliseconds

• Go

  Native unit: integer seconds and nanoseconds

• TypeScript

  Native unit: integer milliseconds

• Ruby

  Native unit: float seconds

• C#

  Native unit: ticks (100 ns)

• Rust

  Native unit: seconds + nanoseconds

• SQL

  Native unit: varies by engine

• Bash

  Native unit: integer seconds

• C++

  Native unit: chrono duration

• Swift

  Native unit: float seconds

• Kotlin

  Native unit: integer milliseconds

• C

  Native unit: time_t seconds

• Perl

  Native unit: integer seconds

• Dart

  Native unit: integer milliseconds

• PowerShell

  Native unit: .NET DateTimeOffset

• Scala

  Native unit: integer milliseconds

• R

  Native unit: float seconds

• Excel

  Native unit: days since 1899-12-30

Why every language does this differently

The underlying value is identical everywhere — an integer counting seconds since 1970 — but each language picked a different default resolution and a different attitude to time zones, and those two choices explain almost every difference in the snippets above.

Native unit	Languages
Seconds	PHP, C, Perl, Ruby, Bash
Milliseconds	JavaScript, TypeScript, Java, Kotlin, Scala, Dart
Float seconds	Python, R, Swift
Seconds + nanoseconds	Go, Rust, C++ (chrono)
Something else entirely	C# (100 ns ticks from year 1), Excel (days from 1899)

The boundary between a millisecond language and a second language is where bugs cluster. A JavaScript front end talking to a PHP or Python back end crosses that boundary on every request, which is why seconds versus milliseconds is worth reading once, properly.