Repeat from completion date?

For tasks that need to be completed at a certain interval, but not on a specific date of the week/month/year, it'd be helpful to have the option to repeat from the completion date instead of the scheduled date. For example, if I plan to get my hair cut every 4 weeks, but ended up getting my most recent haircut after 5 weeks, WeekPlan will tell me to get my haircut again in 3 weeks. Instead, it could schedule the next instance of the task for 4 weeks from the date that I completed it.