Date & Time

Introduction

Almost every real application needs to work with dates and times — a blog post's publish date, a session's expiry time, an invoice due date, or a "posted 3 hours ago" label. PHP has been handling this since its earliest versions, and it offers two complementary approaches: a set of simple built-in functions, and a more powerful object-oriented DateTime class.

In this lesson, you will learn both styles: the classic date() and time() functions for quick formatting, and the modern DateTime class for anything more involved, along with strtotime() for turning human-readable text into a usable date.

Unix Timestamps with time()

Internally, PHP (like most programming languages) represents a moment in time as a Unix timestamp: the number of seconds that have elapsed since January 1, 1970, 00:00:00 UTC. The time() function returns this value for the current moment.

<?php
$now = time();
echo $now;
// Example output: 1785000000 (an integer, seconds since 1970)

1785000000

A raw timestamp is not very readable on its own, but it is extremely useful for storing dates in a database, comparing two moments in time, or measuring how much time has passed between events.

Formatting Dates with date()

The date() function takes a format string and turns a timestamp into a human-readable string. If you do not pass a timestamp, it uses the current time by default.

<?php
echo date("Y-m-d");
echo "\n";
echo date("H:i:s");
echo "\n";
echo date("Y-m-d H:i:s");

2026-07-26
14:30:00
2026-07-26 14:30:00

You can also format a specific timestamp, rather than the current time, by passing it as the second argument.

<?php
$timestamp = time();
echo date("l, F j, Y", $timestamp);
// Example: Sunday, July 26, 2026

Sunday, July 26, 2026

Common Format Characters

The date() function reads its format string one character at a time, replacing recognized letters with pieces of the date. Here are the ones you will use most often.

The DateTime Class

The date() and time() functions are quick and convenient, but for anything more involved — comparing dates, calculating differences, or doing arithmetic — the object-oriented DateTime class is the more modern and flexible approach.

<?php
$now = new DateTime();
echo $now->format("Y-m-d H:i:s");
echo "\n";

$specificDate = new DateTime("2026-12-25");
echo $specificDate->format("l, F j, Y");

2026-07-26 14:30:00
Friday, December 25, 2026

The DateTime constructor accepts almost any human-readable date string, and its format() method uses the exact same format characters you just learned for date(). This makes DateTime feel familiar while opening the door to more advanced operations, like comparing two dates directly.

<?php
$date1 = new DateTime("2026-01-01");
$date2 = new DateTime("2026-12-25");

if ($date2 > $date1) {
    echo "date2 is later than date1";
}

date2 is later than date1

Parsing Strings with strtotime()

Often you will have a date as plain text — from a form, a file, or an API — and need to convert it into something PHP can work with. The strtotime() function parses a wide variety of human-readable date and time formats into a Unix timestamp.

<?php
$timestamp = strtotime("2026-12-25");
echo date("Y-m-d", $timestamp);
echo "\n";

$timestamp2 = strtotime("next Monday");
echo date("Y-m-d", $timestamp2);
echo "\n";

$timestamp3 = strtotime("+1 week");
echo date("Y-m-d", $timestamp3);

2026-12-25
2026-07-27
2026-08-02

strtotime() understands relative phrases like "tomorrow", "next Monday", "+1 week", and "-3 days", in addition to standard date formats. If it cannot understand the input, it returns false, so it is a good idea to check the result before using it.

Date Arithmetic

A common task is calculating a date relative to another one, such as "7 days from now" or "one month before this invoice date." PHP gives you two convenient ways to do this: passing a relative string to strtotime(), or using the DateInterval class with DateTime.

<?php
$tomorrow = strtotime("+1 day");
echo date("Y-m-d", $tomorrow);

2026-07-27

The DateTime approach uses the modify() method or a DateInterval object, which is often clearer when working with an object you already have.

<?php
$date = new DateTime("2026-07-26");
$date->add(new DateInterval("P7D")); // P7D means "a period of 7 days"
echo $date->format("Y-m-d");
echo "\n";

$date->sub(new DateInterval("P2D")); // subtract 2 days
echo $date->format("Y-m-d");

2026-08-02
2026-07-31

Common Mistakes

Best Practices

Frequently Asked Questions

Key Takeaways

Summary

Working with dates and times is a routine part of almost every PHP application. The simple date() and time() functions cover quick formatting needs, while the DateTime class gives you a more powerful, object-oriented toolkit for comparisons and arithmetic, and strtotime() bridges the gap between human-readable text and usable timestamps.

Next, you will look at how PHP handles errors at a fundamental level — the traditional error system that existed long before exceptions became the preferred approach.