title: Adding days to specific day
body: <p>Many examples are about adding days to this day. But how to do it, if I have different starding day?</p>
  
  <p>For example (Does not work):</p>
  
  <pre><code>$day='2010-01-23';
  
  // add 7 days to the date above
  $NewDate= Date('$day', strtotime("+7 days"));
  echo $NewDate;
  </code></pre>
  
  <p>Example above does not work. How should I change the starding day by putting something else in the place of Date?</p>