Will Cpanel's Dec 2018 PHP switch off break my Joomla website?

Short answer

Cpanel (leading webhosting software) and PHP (the "operating system" for your website) will drop support for older PHP versions from Dec 2018. Current versions of Joomla, Wordpress and Opencart will be fine. Older versions may have isssues or just stop working all together. This is because older versions of Joomla, Wordpress and OpenCart were only written and tested to work on past PHP versions.

Now is a great time to talk to Artful about upgrading your site software to the latest version. We can also help you run a custom older PHP version to keep your site on the air. This is a short term "bandaid fix". Adding and switching to an older custom PHP version is not expensive but has issues for your website's security, speed and reliability.

 Longer nerdier answer

What exactly are Cpanel, PHP, Joomla, Wordpress and OpenCart? Why should I care?

Cpanel is the main webhosting software used around the world. If you have a website and email chances are you're using Cpanel to make this happen. (Artful uses Cpanel for all our webhosting clients.) 

Joomla, Wordpress and OpenCart are all CMS software. In plain english a CMS lets non nerds (and us web nerds too) update your content and allows your clients to see, find and buy your stuff online.

PHP is similar to the operating system on your computer eg Mac OSX or Windows 10. Joomla, Wordpress and OpenCart (and virtually all web software) run under PHP. Just like your computer, PHP has regular security updates and occasional major version updates. Also, just like on your computer, older versions of software eg Word are not guranteed to work on newer operating system versions. Even minor security updates can lead to bugs that need to be fixed.

How is PHP 7 better for my website?

The main reason to keep software updated is always security. Up to date sites basically never get hacked! To be safe all components need to be updated ie PHP, CMS (Joomla Wordpress and OpenCart) and all add-ons or plugins on your website. PHP 7 is more secure itself and also forces all program developers to be more secure as well.

PHP 7 also makes sites a lot faster for your visitors. 

More information

https://blog.cpanel.com/removal-of-php-5-4-and-php-5-5-in-easyapache-profiles/

http://php.net/supported-versions.php