PHP versions 5.x, PHP 7.0.x, 7.1.x & 7.2.x (as well as all earlier versions) have now stopped receiving security patches.
Any security vulnerabilities discovered in these out of date versions of the software will likely go unpatched.
This means that any attempt to hack your website is going to be a lot easier! You don't have to be running a famous dot com website in order to get hacked; most hacking is done in a somewhat arbitrary automated way by software that doesn't differentiate between large and small websites.
Aside from security concerns, another very important reason for updating PHP is to improve the speed of your website. Page load time is a metric in Google's search engine and so a slow loading page may give you a disadvantage over competitor websites.
So for both your website's security and SEO rankings keeping your website up to date is something you should do all you can to keep on top of. Don't assume that your ISP is doing this for you, it is very likely not the case.
If you are unsure about your exact PHP version check with our free PHP version checking tool now and follow the steps we recommend.
If you've already done that but we are unable to determine the version of PHP on your server check this article on how to manually determine your website's PHP version.
For further details on the EOL (end of life) date for each version of php see this table on the official PHP website
If you now know that you are running an old version of PHP on your web server follow our guide on how to get it updated.
If you want to know when a specific version of PHP will stop receiving updates and become vulnerable check here.