The "windfall elimination provision" affects how the amount of your retirement or disability benefits is calculated if you receive a pension from work where Social Security taxes were not taken out of your pay. A modified formula is used to calculate your benefit amount, resulting in a lower Social Security benefit.
The reduction in your Social Security benefit cannot be more than one-half of that part of your pension based on your earnings after 1956 from which Social Security taxes were not deducted. The Federal Ballpark E$timate uses the maximum windfall elimination provision to estimate your social security benefits. This will give you a conservative estimate. You can learn more about the windfall elimination provision at: https://www.ssa.gov/pubs/10045.html