Social Security tax overpayment

My son had a part-time job. he earned 1993.69 and had $123.61 withheld as social security tax. Turbo-Tax says this was too much and the amount should be $74.03.  But 123.61 is 6.2% of 1993.69, so it seems to me that the amount withheld was correct. Am I missing something? this seems like a pretty basic function that Turbo tax would get right.  This was his only wage income.