6. An older sibling has an overfunded plan: "Since the unused dollars in a 529 plan for an older sibling can be transferred to a younger sibling's plan, this may be a reason to stop 529 contributions for the younger child," O'Brien says.
For example, an older sibling has an account balance of $40,000 after completing college. The younger sibling has $10,000 and two years left at a university where the annual cost of attendance is $25,000. The younger sibling could use the older sibling's remaining account balance.