Hi. My mother will turn 66 in March 2017. If she wants to apply for SS, does she need to do so three months before her actual birth date? If she does not do so, does she then have to wait until the following year?
No. Your mother could file her application anytime between now and the end of September 2017 and still be able to elect March 2017 as her month of entitlement. This is because applications filed after full retirement age can be retroactive for up to 6 months.
Before filing, however, your mother may want to consider running the maximization software available on this website. She may have other, more advantageous, filing options available.