Note:

The employee social security taxes reported on lines 5a(i) and 5a(ii) should not be included in the Line 13b calculation for the employer share of social security tax, however, these lines can be used to calculate the employee share of social security tax deferred. The amount reported on line 13b shouldn’t be reduced by any credits claimed on line 11a, 11b, or 11c. Tax that has already been paid cannot be deferred, therefore, the maximum amount that can be deferred each quarter is the smaller of (1) the employer share of social security tax and/or the employee share of social security tax, or (2) the excess of line 10 (reduced by the amount, if any, on line 11a) and line 13a.