Calculate Fortnight Date

The following code will calculate a recurring fortnightly date from a given date, i.e. a star-date. The date format should be 'Y-m-d' for the following code. However, you can make updates in it as per requirements.

For example: The start date for the fortnight cycle date was set to be as "2018-01-10". Then, as per current cycle, next will be 2018-02-20.