How to Find the Number of Days Between Two Dates in PHP

By the end of this page, you will understand how to calculate the number of days between two dates in PHP, especially using DateTime and diff(). You will also learn how the result works, how to handle date order, and what mistakes to avoid when working with dates.

In PHP, the safest and most readable way to find the number of days between two dates is to use the DateTime class together with the diff() method.

DateTime represents a date and time value, and diff() compares two DateTime objects and returns a DateInterval object. That interval contains useful information such as:

• years
• months
• days
• hours
• whether the result is negative

For day differences, the most useful property is often days, which gives the total number of days between the two dates.

This matters because dates are more complicated than simple numbers. Different months have different lengths, leap years exist, and time zones can affect results. PHP's built-in date classes handle these rules for you, which makes your code more accurate and easier to maintain.

A common beginner approach is to subtract Unix timestamps and divide by 86400, but that can become unreliable when time zones or daylight saving changes are involved. For most application code, DateTime is the better choice.

Think of two dates as two points on a calendar.

Using DateTime and diff() is like asking PHP to count the calendar distance between those two points for you.

Instead of manually counting days or doing math with seconds, you hand both dates to PHP and say:

• "Here is the start date"
• "Here is the end date"
• "Tell me the difference"

PHP then returns the gap in a structured way, much like a travel summary:

• 0 years
• 2 months
• 5 days
• total: 66 days

This is easier and safer than trying to do calendar math by hand.

Basic syntax

$date1 = new DateTime('2024-01-01');
$date2 = new DateTime('2024-01-10');

$interval = $date1->diff($date2);

echo $interval->days;

This prints:

9

Why it works

• new DateTime('2024-01-01') creates the first date
• new DateTime('2024-01-10') creates the second date
• $date1->diff($date2) compares the two dates
• $interval->days gives the total difference in days

Example with formatted output

<?php
$start = new DateTime('2024-03-01');
$end = new DateTime('2024-03-15');

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

echo "Days between dates: " . $interval->days;

Output:

Days between dates: 14

Example when dates are reversed

<?php
$date1 = new DateTime('2024-03-15');
$date2 = new DateTime('2024-03-01');

$interval = $date1->diff($date2);

echo $interval->days;

Output:

14

The days property is the absolute total number of days. If you also want to know whether the result is negative, check the invert property:

<?php
$date1 = new DateTime('2024-03-15');
$date2 = new DateTime('2024-03-01');

$interval = $date1->diff($date2);

echo $interval->days;   // 14
echo "\n";
echo $interval->invert; // 1 means date1 is later than date2

Older timestamp-based approach

<?php
$date1 = strtotime('2024-01-01');
$date2 = strtotime('2024-01-10');

$days = ($date2 - $date1) / 86400;

echo $days;

This can work for simple cases, but DateTime is generally preferred for clarity and correctness.

Example

<?php
$start = new DateTime('2024-05-01');
$end = new DateTime('2024-05-06');

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

echo $interval->days;

Step by step

1. PHP creates a DateTime object for 2024-05-01.
2. PHP creates another DateTime object for 2024-05-06.
3. $start->diff($end) compares the two dates.
4. PHP builds a DateInterval object containing the difference.
5. $interval->days reads the total number of days in that difference.
6. The result 5 is printed.

Trace

Important note

The difference is based on the actual dates, not on manually counting strings or splitting text. That is why this approach is more reliable.

Calculating the number of days between dates is common in real applications.

Common examples

• Booking systems: number of nights between check-in and check-out dates
• Subscription apps: days left until renewal or expiration
• Task management tools: days remaining until a deadline
• Reporting dashboards: difference between start and end dates for a report range
• HR systems: leave duration between two dates
• Invoice systems: payment overdue by a certain number of days

Example: subscription expiration

<?php
$today = new DateTime('today');
$expiresAt = new DateTime('2024-12-31');

$interval = $today->diff($expiresAt);

echo "Days remaining: " . $interval->days;

Example: hotel booking

<?php
$checkIn = new DateTime('2024-08-10');
$checkOut = new DateTime('2024-08-15');

$nights = $checkIn->diff($checkOut)->days;

echo "Total nights: " . $nights;

In both cases, PHP handles the calendar rules for you.

In real PHP projects, developers usually wrap date calculations in small helper functions or service classes so the logic stays consistent across the codebase.

Common patterns

Validation before calculation

Developers often validate input before creating DateTime objects.

<?php
function daysBetween(string $date1, string $date2): int
{
    $start = new DateTime($date1);
    $end = new DateTime($date2);

    return $start->diff($end)->days;
}

Guard clauses

If input may be missing, guard clauses keep the function safe.

<?php
function daysBetweenOrNull(?string $date1, ?string $date2): ?int
{
    if (!$date1 || !$date2) {
        return null;
    }

    $start = new DateTime($date1);
    $end = new DateTime($date2);

    return $start->diff($end)->days;
}

Keeping the sign when needed

Sometimes developers need to know whether a date is in the past or future.

<?php
function signedDaysBetween(string $date1, string $date2): int
{
    $start = new DateTime($date1);
    $end = new DateTime($date2);
    $interval = $start->diff($end);

    return $interval->invert ? -$interval->days : $interval->days;
}

Using normalized dates

In many apps, developers normalize to midnight or use date-only values to avoid unexpected time effects.

<?php
$start = new DateTime('2024-06-01 00:00:00');
$end = new DateTime('2024-06-10 00:00:00');

This is especially useful in billing, scheduling, and reporting code.

1. Using raw second math for all cases

Broken example:

<?php
$days = (strtotime($date2) - strtotime($date1)) / 86400;

Why this can be a problem:

• daylight saving changes can affect the exact number of seconds in a day
• times may not both be midnight
• the result may be fractional

Better approach:

<?php
$days = (new DateTime($date1))->diff(new DateTime($date2))->days;

2. Forgetting that time affects the result

<?php
$date1 = new DateTime('2024-01-01 23:00:00');
$date2 = new DateTime('2024-01-02 01:00:00');

$interval = $date1->diff($date2);
echo $interval->days;

This may print 0 because the total difference is only 2 hours, not a full day.

If you only care about dates, use date-only values or set both times to midnight.

3. Expecting days to be negative

<?php
$date1 = new DateTime('2024-03-10');
$date2 = new DateTime('2024-03-01');

$interval = $date1->diff($date2);
echo $interval->days;

$interval->days is usually the absolute number of days. To check direction, use:

<?php
echo $interval->invert;

4. Trusting invalid date strings

Broken example:

<?php
$date = new DateTime('tomoroww');

Always validate user input when dates come from forms or APIs.

5. Mixing time zones accidentally

If one date uses one time zone and another uses a different time zone, results may differ from what you expect.

<?php
$utc = new DateTime('2024-01-01', new DateTimeZone('UTC'));
$local = new DateTime('2024-01-02', new DateTimeZone('America/New_York'));

When accuracy matters, use the same time zone for both dates.

Comparing common approaches

DateTime vs strtotime()

Absolute days vs signed days

Quick reference

Create dates

$date1 = new DateTime('2024-01-01');
$date2 = new DateTime('2024-01-10');

Get difference

$interval = $date1->diff($date2);

Total days

echo $interval->days;

Check direction

echo $interval->invert;

• 0 = first date is earlier or same
• 1 = first date is later

Signed result

$signedDays = $interval->invert ? -$interval->days : $interval->days;

Simple helper function

function daysBetween(string $a, string $b): int
{
    return (new DateTime($a))->diff(new DateTime($b))->days;
}

Best practice

• Prefer DateTime over manual second math
• Use the same time zone when comparing dates
• If you only care about dates, avoid including times
• Validate user input before calculation

Edge cases

• Same date returns 0
• Reversed dates still give positive days
• Time values can change the result
• Daylight saving transitions can affect timestamp math

How do I calculate days between two dates in PHP?

Use DateTime and diff():

$days = (new DateTime('2024-01-01'))->diff(new DateTime('2024-01-10'))->days;

What does $interval->days mean in PHP?

It is the total number of days between two dates in the DateInterval result.

Can diff() return a negative number of days?

The days property is usually absolute. To detect direction, check $interval->invert.

Is strtotime() good for finding date differences?

It can work for simple cases, but DateTime is usually a better and safer choice.

Why do I get 0 days when the dates are on different calendar dates?

Because the time difference may be less than 24 hours. If you only care about dates, compare date-only values or set both times to midnight.

How do I get signed day difference in PHP?

Use both days and invert:

$signed = $interval->invert ? -$interval->days : $interval->days;

Does PHP handle leap years automatically?

Yes. DateTime and diff() handle normal calendar rules, including leap years.

• DateTime — The main PHP class for working with dates and times.
• DateInterval — The object returned by diff(), containing the date difference.
• DateTimeZone — Important when comparing dates across time zones.
• strtotime() — A simpler alternative that converts date strings into timestamps.
• Unix timestamp — Useful for understanding older date-difference techniques.
• Input validation — Important when dates come from forms, APIs, or user input.
• PHP date formatting — Often used together with date calculations when displaying results.