How Do FICA Taxes Show Up in Holistiplan?
Usually, they will not; but you can add them in Scenario Analysis!
FICA (the acronym for Federal Insurance Contributions Act) Taxes are deducted from a wage earner's paycheck to cover contributions to Social Security and Medicare. Those Social Security Wages and Medicare Wages are reported in Boxes 3 and 5, respectively, as outlined in blue and red on the sample Form W-2 below. 
Because this is a payroll tax and not technically part of your income tax, Holistiplan will not read in anything related to FICA from an uploaded tax return, with two exceptions - Additional Medicare Taxes and Self Employment Tax.
Additional Medicare Taxes - This occurs when a taxpayer will have excess Medicare tax withheld of 0.9% (as reported on Form 8959) on wages in excess of $200k for single filers, $250k for married filing jointly filers, or $125k for married filing separately filers. In that case, you may wish to enter the amount of that withholding in the Other row after expanding the Total Withholding section at the bottom of the Scenario Analysis screen.

Withholdings for FICA (line 4 of the W-2) would not be entered into the Total Withholding section, as that would overstate the total withholdings for income tax purposes.
Self-Employment Taxes - This occurs for self-employed (SE) individuals who pay those Social Security and Medicare taxes in the form of SE Taxes that are calculated on Schedule SE, and are reported on Schedule 2.
Aside from these two exceptions, FICA will not populate in Holistiplan from an uploaded return. However, users can account for FICA Taxes as seen below by making some entries within the Wages Worksheet. 
Once the wage entries are broken out within the Wages Worksheet, a FICA Tax amount weill populate within the FICA section of Scenario Analysis. The Total Tax refers to line 24 of Form 1040, only including taxes represented on the tax return, while the Tax Plus FICA adds the Total Tax from the return and FICA Taxes paid via payroll deductions into a combined tax figure.