When upgrading web software, one of the first issues you need to deal with is whether the new of the software is compatible with the PHP version you are using or if you need to make a change. With PrestaShop, that has become more complicated as the range of PHP versions being supported has shrunk with recent releases. Version 1.6.1.x supported PHP versions from 5.2 to 7.1. The latest version, 1.7.7.x, only supports PHP 7.1 to 7.3.
Figuring out what versions of PHP are supported by PrestaShop is not made as easy as can be. PrestaShop does provide a chart (current as of when this was posted):
But it isn’t given its own page on PrestaShop’s website, instead you have to scroll down on the “System requirements for PrestaShop 1.7” page to find it.
That doesn’t tell the entire story though, since, for example, if you are running an older version of PrestaShop 1.6.1.x it won’t include PHP compatibility updates for newer versions of PHP that were included in later releases.
Managing PHP Version Differences
If you are keeping PrestaShop up to date, you usually shouldn’t run into PHP version compatibility issues. If you have a more out-of-date PrestaShop version that needs to be brought up to date, then you are more likely to run into issues. That is one of the many reasons why you should do a test of the upgrade first, since it makes it easier to handle any issues like that. In the best-case scenario, your web hosting setup allows running different PHP versions in different website directories and the various versions of PHP you need access to are available. Things get more complicated when either of those are not true.
How PHP Version Support is Determined?
If you are wondering how the developers of PrestaShop decide which versions of PHP to support, you can find a detailed explanation here. The short version is that it is based on what versions of PHP are currently supported and what versions of PHP are supported by software that PrestaShop depends on.