All tax table data is provided in a separate data file (typically "us.dat"), which is updated via the TaxUpdate subscription service. Your application must specify the path to this file in the DataFilename property.

Because there are many taxes within the tax table data, the developer must indicate which tax is to be computed. This is accomplished by passing the name of the desired tax to the SelectedTax property. The computed tax is returned by the TaxAmount method.

Another issue to be addressed is the PayDate property. In some cases, more than one version of a particular tax exists (possibly for two different years), so the developer should set the PayDate equal to the desired check date for the payroll. This will ensure that the formula corresponding to that date is applied in calculations.

Several vital employee information items must be supplied by setting properties. The key input properties required for most tax computations are:

• Earnings
• Exemptions and StateExemptions
• FilingStatus

Other input items, such as the Miscellaneous, Auxiliary, YTDEarnings, StateExemptions, UnemploymentRate, or Supplemental properties may be required for certain taxes or special situations.

The computed tax is returned by the TaxAmount method.

Other properties such as Instructions, Withheld, etc., are informational only, and not related to actual calculation of withholding taxes. These are useful in presenting input forms or reports to the end user.