Add & Subtract Days Weeks Months To A Date In PHP

Welcome to a quick tutorial on how to add and subtract days, weeks, months to a date in PHP. So you need to do some “date yoga” in your project?

There are 3 common ways to add and subtract from a date in PHP:

Create a date-time object, then use the modify function.
- $dt = new DateTime("2019-08-14");
- $dt->modify("+4 days");
- $dt->modify("-1 week");
Use the strtotime() function.
- $date = "2019-08-14";
- $add = date("d M Y", strtotime($date . "+1 week"));
- minus = date("d M Y", strtotime($date . "-2 months"));
Manually calculate using the Unix timestamp.
- $unix = strtotime("2019-08-14");
- $add = date("d M Y", $unix + (2*86400));
- $minus = date("d M Y", $unix - (14*86400));

That covers the basics, but let us walk through more examples in this guide – Read on!

DOWNLOAD & NOTES

Here is the download link to the example code, so you don’t have to copy-paste everything.

EXAMPLE CODE DOWNLOAD

Source code on GitHub Gist

Just click on “download zip” or do a git clone. I have released it under the MIT license, so feel free to build on top of it or use it in your own project.

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ADD & MINUS TO DATE

All right, let us now get into the examples of how to add/minus days, weeks, months to a date in PHP.

1) DATE TIME OBJECT

1-date-time.php

<?php
// (A) CREATE NEW DATE TIME OBJECT
$dt = new DateTime("2019-08-14");
echo "ORIGINAL DATE: " . $dt->format("d M Y") . "<br>";
 
// (B) ADD DAYS WEEKS MONTHS
$dt->modify("+4 days");
echo "+4 DAYS: " . $dt->format("d M Y") . "<br>";
$dt->modify("+2 weeks");
echo "+2 WEEKS: " . $dt->format("d M Y") . "<br>";
$dt->modify("+1 month");
echo "+1 MONTH: " . $dt->format("d M Y") . "<br>";
 
// (C) SUBTRACT DAYS WEEKS MONTHS
$dt->modify("-2 days");
echo "-2 DAYS: " . $dt->format("d M Y") . "<br>";
$dt->modify("-1 week");
echo "-1 WEEK: " . $dt->format("d M Y") . "<br>";
$dt->modify("-2 months");
echo "-2 MONTHS: " . $dt->format("d M Y") . "<br>";

This should be self-explanatory. The new DateTime(TIMESTAMP) object is probably one of the most painless and “human” ways to manipulate a given date. Simply use the format() function to add or subtract a range of days, weeks, months, years from the timestamp.

2) STRING TO TIME

2-strtotime.php

<?php
// (A) ORIGINAL DATE
$date = "2019-08-14";
echo "ORIGINAL DATE: $date<br>";
 
// (B) ADD DAYS WEEKS MONTHS
$added = date("d M Y", strtotime($date . "+4 days"));
echo "+4 DAYS: $added<br>";
$added = date("d M Y", strtotime($date . "+2 weeks"));
echo "+2 WEEKS: $added<br>";
$added = date("d M Y", strtotime($date . "+1 month"));
echo "+1 MONTH: $added<br>";
 
// (C) SUBTRACT DAYS WEEKS MONTHS
$added = date("d M Y", strtotime($date . "-4 days"));
echo "-4 DAYS: $added<br>";
$added = date("d M Y", strtotime($date . "-2 weeks"));
echo "-2 WEEKS: $added<br>";
$added = date("d M Y", strtotime($date . "-1 month"));
echo "-1 MONTH: $added<br>";

Yep, another simple one. This is actually a combination of using the strtotime() function to add/subtract the date, then using date() to get the date format that you want. I will leave links in the summary below on how date() works.

3) UNIX TIMESTAMP

3-unix.php

<?php
// (A) UNIX TIMESTAMP
// UNIX TIMESTAMP = NUMBER OF SECONDS SINCE 1 JAN 1970
$unix = strtotime("2019-08-14");
// 1 DAY = 24 HRS * 60 MINS * 60 SECS = 86400 SECS
$day = 86400;

// (B) ADD DAYS WEEKS MONTHS
echo "+4 DAYS: " . date("d M Y", $unix + (4*$day)) . "<br>";
echo "+2 WEEKS: " . date("d M Y", $unix + (14*$day)) . "<br>";
// BE CAREFUL: 1 MONTH MAY NOT BE EXACTLY 30 DAYS
echo "+1 MONTH: " . date("d M Y", $unix + (30*$day)) . "<br>";

// (C) SUBTRACT DAYS WEEKS MONTHS
echo "-3 DAYS: " . date("d M Y", $unix - (3*$day)) . "<br>";
echo "-2 WEEKS: " . date("d M Y", $unix - (14*$day)) . "<br>";
echo "-1 MONTH: " . date("d M Y", $unix - (30*$day)) . "<br>";

Lastly, for you guys who do not know – strtotime(TIMESTAMP)actually returns a Unix timestamp. That is, the number of seconds that have elapsed since 1 Jan 1970 UTC. So to add and subtract days/weeks/months with the Unix Timestamp is a very Mathematical process.

Essentially, one day has 24 hours (or 86400 seconds).
So for example, if we want to add 3 days to a timestamp, that will be $unix += 3 * 86400;
Another example, if we want to add 2 weeks, that will be 14 days – $unix += 14 * 86400.

Yep, you catch the drift.

EXTRAS

That’s all for this tutorial, and here is a small section on some extras that may be useful to you.

WHICH IS THE BEST?

Personally, I am leaning toward DateTime and strtotime for convenience. But the performance of these 2 is not exactly amazing… Manually calculating with the Unix timestamp is not all bad, and it has an edge when it comes to processing in a loop – for ($i=1; i<14; i++) { $timestamp += 86400; }

SUMMARY – ALL THE COMMON DATE/TIME FUNCTIONS

Function	Description	Reference
`$DATETIME = new DateTime(STRING)`	Create a new date-time object. Takes the current server time by default, or you can provide a date/time string.	Click Here
`$DATETIME->format(STRING)`	Formats the date-time object.	Predefined Standards Manual Format
`$DATETIME->modify(STRING)`	Add minutes, hours, days, weeks, months, years, from the given date/time.	Click Here
`strtotime(STRING)`	Gets the Unix timestamp from the given date string.	Click Here

THE END

Thank you for reading, and we have come to the end of this guide. I hope that it has helped you to understand better, and if you want to share anything with this guide, please feel free to comment below. Good luck and happy coding!

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