Most people know that applying for Social Security at different ages can make a huge difference. But many don't realize that waiting a month or two can also change your benefits.

In the latest installment of our Social Security Q&A video series, Dan Caplinger, The Motley Fool's director of investment planning, takes a question from Dave, who says he's turning 66 in August and isn't sure whether to apply for Social Security then or wait until the beginning of 2015. Dan notes that you're entitled to benefits in the first month in which you're the appropriate age for the entire month, so unless Dave's birthday is deemed to be the first day of the month, he'll be eligible for full retirement age benefits in September. But if Dave waits until January, he'll get four months' worth of delayed retirement credits, which will boost his monthly payments by about 2.7%. Dan concludes that the Social Security Administration lets you apply for benefits up to four months before you want them to start, so it's up to you to decide whether it makes sense to wait and get greater benefits or to start getting checks sooner.