If your pension is from work where you paid Social Security taxes, it will not affect the amount of your Social Security benefit. Pensions based on work that is not covered by Social Security (for example, the Federal civil service and some State or local government agencies) probably will cause the amount of your Social Security benefit to be reduced. This type of benefit reduction is called the Windfall Elimination Provision  (WEP).

If you will receive a pension for work not covered by Social Security (such as government employment), any Social Security benefits you may be eligible to receive on your spouse's record may also be reduced.  This type of benefit reduction is called Government Pension Offset  (GPO).

Social Security also has Websites with Information for Government Employees, that includes a WEP calculator, and a GPO page which includes a GPO calculator.

You also can get information about the Windfall Elimination Provision (WEP) when you visit Social Security Online's Retirement Planner Be sure to click on "Learn about factors that may affect my retirement benefits" (see first page of the Planner). Among other facts, you can learn the maximum monthly amount your benefit may be reduced because of WEP and the calculation of your retirement benefit.