If you switch plans mid-year — due to a job change, for example — you'll typically find that you start over with a new deductible on the new plan. It's possible for exceptions to be made if there are extenuating circumstances, such as an insurer becoming insolvent mid-year, or an insurer offering a deductible carry-over credit when a person switches to another plan offered by the same insurer. But exceptions like that are not common. Deductibles are not prorated. So you'll still have a full deductible to meet for the remainder of the plan year before you receive post-deductible benefits, even if you join the plan mid-way through the plan year.