What does a payroll system involve?
You would need to be able to calculate the tax withheld based on formulas. These formulas’ are determined by the employees filing status (married or single) and the number of allowances (erroneously called exemptions by many) the employee claimed. What state is the employee being paid in? Each state has a different rate (if it has income tax) and some states allow the local municipality to collect income tax (NYC). But as the tax bracket changes, so do the percentages used in the formulas. And with social security there is a top limit of gross payroll that’s taxed while the medicare portion has no top limit. Then there is EITC – Earned Income Tax Credit. If an employee qualifies, the employer must include the EITC in the employees weekly payroll. It is a way for the government to get the EITC to the poor weekly instead of once a year. Of course this translates into a credit for the employer. And I’m sure there is a host of other issues not mentioned here; eg pretax deductions, taxable
