title: How to handle date and time with PHP?
body: <p>I need to do a little bit more complicated calculations with time and date values from my MySQL database with PHP. </p>
  
  <p>I need to add or substract different values from a given date. </p>
  
  <p>For example:</p>
  
  <ul>
  <li>Substracting 1 Month</li>
  <li>Substracting 30 Days</li>
  <li>Substracting 4 Weeks</li>
  <li>Adding 4 Month</li>
  <li>Adding 3 Month</li>
  <li>Adding 90 Days</li>
  <li>Adding 2 Years</li>
  </ul>
  
  <p>Please note that there is a difference between substracting 1 Month, 4 Weeks or 30 Days.</p>
  
  <p>What's the preferred way of doing this? Is there any clever library or can I do this with PHP's own functions?</p>