These PHP examples use Unix seconds for the portable baseline and show milliseconds only where the runtime exposes them naturally. The question to answer before copying a snippet is simple: what unit does the next API expect?

Get the current Unix time

$seconds = time();
$milliseconds = (int) floor(microtime(true) * 1000);

Convert a timestamp to UTC

$date = (new DateTimeImmutable("@1700000000"))
  ->setTimezone(new DateTimeZone("UTC"));
echo $date->format(DateTimeInterface::ATOM);

Production note

The @ prefix creates a Unix-timestamp DateTimeImmutable. Set the display timezone explicitly after construction.

Keep the unit in the field name when a value crosses a boundary: createdAtSeconds and createdAtMs are longer than createdAt, but much less mysterious during an incident.

Epoch to DateDate to EpochTimezone ConverterAll Code Snippets

Frequent questions:

Q: Does time() include milliseconds?
A: No. time() returns whole Unix seconds. Use microtime(true) if you need fractional seconds or if you need to calculate a millisecond timestamp.
Q: Why use gmdate() instead of date()?
A: gmdate() formats the timestamp in UTC. date() uses the server's configured timezone, which can change between local development, containers, and production hosting.
Q: How do I check a PHP conversion?
A: Convert the same value with gmdate('c', $timestamp), then compare it with an independent epoch converter or a database UTC function before using it in a migration.