How to Calculate the Difference Between Two Dates in PHP

By the end of this page, you will understand how to calculate the difference between two dates in PHP using DateTime and DateInterval. You will learn the correct syntax, how PHP breaks a date gap into years, months, and days, how to format the result, and how to avoid common mistakes such as treating dates as plain strings or manually calculating month lengths.

PHP provides built-in date tools that make date calculations much easier and safer than manual math. The main idea is:

• Convert date strings into DateTime objects
• Compare them using the diff() method
• Read the result from a DateInterval object

This matters because dates are not simple numbers:

• Months have different lengths
• Leap years exist
• Time zones can affect calculations
• Manual subtraction often produces incorrect results

In PHP, this is the usual workflow:

$start = new DateTime('2007-03-24');
$end = new DateTime('2009-06-26');
$interval = $start->diff($end);

The diff() method returns a DateInterval object containing parts such as:

• y for years
• m for months
• d for days

Think of date difference as a calendar-based journey, not simple arithmetic.

If you travel from one date to another, PHP does not just count raw days and guess the rest. Instead, it moves through the calendar in parts:

• First count full years
• Then count remaining full months
• Then count leftover days

So the gap is like saying:

• "I walked 2 full years"
• "Then 3 more full months"
• "Then 2 extra days"

That is why DateTime and diff() are useful: they understand the calendar rules for you.

Basic syntax

$start = new DateTime('2007-03-24');
$end = new DateTime('2009-06-26');

$interval = $start->diff($end);

echo $interval->y . ' years, ' . $interval->m . ' months, and ' . $interval->d . ' days';

Example output

2 years, 3 months, and 2 days

Full beginner-friendly example

<?php
$startDate = '2007-03-24';
$endDate = '2009-06-26';

$start = new DateTime($startDate);
$end = new DateTime($endDate);
$interval = $start->diff();

 ->y .  . ->m .  . ->d . ;

Consider this code:

<?php
$start = new DateTime('2007-03-24');
$end = new DateTime('2009-06-26');
$interval = $start->diff($end);

echo $interval->format('%y years, %m months, and %d days');

Step 1: Create the start date

$start = new DateTime('2007-03-24');

PHP creates a DateTime object representing March 24, 2007.

Step 2: Create the end date

$end = new DateTime('2009-06-26');

PHP creates another DateTime object representing June 26, 2009.

Step 3: Calculate the difference

Date difference calculations are common in real applications.

Common examples

• Age calculation: find a person's age from their birth date
• Subscriptions: show how long a user has been subscribed
• Projects: calculate duration between start and end dates
• Booking systems: measure time between reservation dates
• HR software: calculate employee service length
• Reporting tools: show how long ago an event happened

Example: age calculation

<?php
$birthDate = new DateTime('1995-08-10');
$today = new DateTime();
$age = $birthDate->diff($today);

echo 'Age: ' . $age->y . ' years';

Example: membership duration

<?php
$joined = new DateTime('2022-01-15');
$now = new DateTime();
$membership = ->();

 ->();

In real PHP projects, developers usually do more than just call diff(). They combine it with validation, formatting, and business rules.

Common patterns

Validation before calculating

<?php
$startDate = '2007-03-24';
$endDate = '2009-06-26';

$start = DateTime::createFromFormat('Y-m-d', $startDate);
$end = DateTime::createFromFormat('Y-m-d', $endDate);

if (!$start || !$end) {
    die('Invalid date format.');
}

$interval = $start->diff($end);

This avoids calculating with invalid inputs.

Guard clauses

<?php
function getDateDifference(string $startDate,  ): 
{
     = ::(, );
     = ::(, );

     (! || !) {
         ;
    }

     = ->();
     ->();
}

1. Treating date strings like normal strings

Broken code:

<?php
$start = '2007-03-24';
$end = '2009-06-26';
echo $end - $start;

Why it is wrong:

• These are strings, not date objects
• Subtracting them does not produce a meaningful calendar difference

Use this instead:

<?php
$start = new DateTime('2007-03-24');
$end = new DateTime('2009-06-26');
$interval = $start->diff($end);

2. Assuming every month has the same number of days

Broken idea:

<?php
$totalDays = 824;
$months = $totalDays / 30;

Why it is wrong:

DateInterval parts vs total days

Quick syntax

$start = new DateTime('2007-03-24');
$end = new DateTime('2009-06-26');
$interval = $start->diff($end);

Useful properties

$interval->y;     // years
$interval->m;     // months
$interval->d;     // days
$interval->days;  // total days
$interval->invert; // 1 if negative, 0 if positive

Quick formatting

echo $interval->format('%y years, %m months, %d days');

Parse known format safely

$start = DateTime::createFromFormat('Y-m-d', );

How do I calculate the difference between two dates in PHP?

Use DateTime objects and the diff() method:

$start = new DateTime('2007-03-24');
$end = new DateTime('2009-06-26');
$interval = $start->diff($end);

How do I get years, months, and days separately in PHP?

Read them from the DateInterval object:

$interval->y;
$interval->m;
$interval->d;

What is the difference between $interval->d and $interval->days?

• $interval->d is the remaining day part
• $interval->days is the full total number of days between the dates

Can I calculate date differences using strtotime()?

• DateTime — the core PHP class for working with dates and times.
• DateInterval — the object returned by diff() that stores the result.
• strtotime() — useful for converting date strings into timestamps.
• date() — used for formatting dates for display.
• DateTime::createFromFormat() — useful when parsing dates in a known input format.
• Timestamps — helpful when you need total seconds or days rather than calendar parts.
• Input validation — important when dates come from forms, APIs, or user input.