I have scanned through the Ask Larry topics and have read your updated Get What's Yours. I still am confused as to what start date I should use on my application so as not to incur a reduction in my benefit or my husband's spousal benefit; my actual birthday or the beginning of the next month. I turn 66 on 4/20/17 and want to begin my benefit. My husband (older) will then restrict his application to spousal until he files at 70.
Social Security applications only ask you what month you want to start benefits, not the day. If you want to receive your full retirement age rate, you should elect to start your benefits effective with April 2017. Your husband should also start his spousal benefits effective with April 2017, assuming that he will be at least age 66 in that month.
Social Security benefits for the month of April are paid in May, and you can file up to 4 months in advance, or as early as this month. If you haven't already done so, you may want to consider running the maximization software available on this website in order to make sure that your choosing the best filing strategy.