If you begin to receive Social Security retirement (or survivor) benefits before you reach full retirement age, money you earn over a certain limit will reduce the amount of your Social Security benefit. In 2018, your benefit will be reduced by $1 for every $2 of earnings in excess of $17,040*
The chart below shows the effect of annual earnings of $10,000, $20,000, and $30,000 on a $12,000 annual Social Security benefit ($1,000 monthly) for someone who hasn't yet reached full retirement age.
Source: Social Security Administration, 2017
*Special rules apply in both the year you reach full retirement age and the year you retire if you have not reached full retirement age.