Update Task 'Due Date' field based on a formula

Update Task 'Due Date' field based on a formula

We have a Workflow rule that creates a Task when a field of the module is edited. The Due Date of this task is set to a date field value of the module. If the value is in the past, we want it to be set in the future. How can we achieve this automatically? As far as I can tell, Task Due Date are only Date fields and we can't add a formula to it.

Ex:If Due  Date is 12/16/2000, make it 12/16/2018