The U.S. Social Security Administration has an online Retirement Estimator that will estimate retirement earnings:

The Retirement Estimator produces estimates that are based on your actual Social Security earnings record. Retirement estimates are just that, estimates. They will vary slightly from the actual benefit you may receive in the future because:

• Your Social Security earnings record is constantly being updated;
  
• Our calculators use different parameters and assumptions (e.g., different stop work ages, future earnings projections, etc.); and
  

Your actual future benefit will be adjusted for inflation.

The website also discusses how the Retirement Planner provides detailed information about"Social Security retirement benefits under current law":

• Looking for information, you can:
  
  
  • Find your retirement age,
    
  • Use the benefit calculators to test out different retirement ages or future earnings amounts,
    
  • Learn about Social Security programs,
    
  • Find out what happens if you work after you retire, and
    
  • Learn how certain types of earnings and pensions can affect your benefits.
    
    
• Already near retirement age, you can:
  
  
  • Discover your retirement options,
    
  • Get information about how members of your family may qualify for benefits,
    
  • Find instructions on how to apply for benefits and what supporting documents you'll need to furnish, and
    
  • Apply for retirement benefits.