Hi @anon47948165 ,
You cannot do this natively in Asana… well at least not completely.
You can create a date field called ‘Audit date’ and a number field called ‘Number of days’ and then put them in a formula field as per below:
That will not affect the due date field, it will simply create a ‘Due date function’ formula field which will display your result.
To automatically map this result to Asana’s native due date field, you will need a 3rd party app such zapier.com make.com or Flowsana.net which has a built in rule in Asana, in the tab ‘External actions’ so it could look like this:
Note, it can even set the due date to skip weekends!