If you and your wife both have insurance through your companies and her birthday is first whose is the primary insurance for the family?

If you sign up for insurance with your company, You have to indicate who is primary subscriber between yourself and wife. If both a wife and a husband sign up with the same company and both have stated they are primary, Your wasting your money. In the insurance world, secondary insurance was purchased because you want coverage for medical cost and pharmacy cost your primary insurance does not cover. Birthdays having nothing to do with who is first. Indicating on the insurance form as subscriber does.