[kjam22]

You'll get a reduced rate. If you are under full retirement age for the entire year, they deduct $1 from your benefit payments for every $2 you earn above the annual limit. For 2015, that limit is $15,720.

Beginning with the month you reach full retirement age, your earnings no longer reduce your benefits, no matter how much you earn.

[DFG]

The 2015 earnings limit in the year of full retirement is $41,880. Social Security will deduct $1 for every $3 over this limit. There is no limit on earnings starting the year after full retirement age.

https://faq.ssa.gov/link/portal/34011/34019/Article/3739/What-happens-if-I-work-and-get-Social-Security-retirement-benefits