Does My 401K Affect Social Security? 
During the accumulation phase social security tax is not applied to the amount of money that you contribute to your 401 -LRB- k -RRB- When you start drawing social security you will find that 15 % of your social security benefit will come to you free of income tax . The remaining 85 % can be taxed based upon a complex formula but that formula includes the money that you receive from your 401 -LRB- k -RRB- . 