A key component in retirement planning is determining how much money you'll need. (After all, how can you determine how much to save unless you know how much you'll need when you're retired?) While you may not realize it, some of your expenses will actually go down or be eliminated. Hopefully your mortgage will be paid off at some point; if not, you may decide to move into a smaller, less expensive home since your children will no longer be living with you. Other expenses may no longer be necessary as well: Child care, life insurance, retirement savings, and even car expenses. As you plan for what you'll need, make sure you take into account what you will no longer need as your lifestyle changes.