title: How to get Date 6 month back from now
body: <p>I am developing an app for iPhone. I want to calculate 6 month older date from now.</p>
  
  <p>I tried many ways but can't find any good solution. Can someone assist me to do this.</p>
  
  <p>For example today is 21 October then I want date 6 month back from this that is : 21 April</p>