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The Symmetry Tax Engine (STE) turns an employee’s addresses, wages, and pay details into the exact payroll taxes to withhold for a given paycheck. Whether you use the hosted Web API or the on-premise SDK, every calculation follows the same underlying model: resolve locations, discover which taxes apply, then compute withholding.

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The calculation model

At the highest level, using the STE has three parts.
1

Find location codes

Before the STE can do anything with an employee’s home and work addresses, those addresses must be converted into usable location codes using the Symmetry Location Service (SLS).Location codes change infrequently, so to maximize your annual allotment of SLS calls, store the codes locally within your system and only refresh them at regular intervals or whenever an employee changes addresses.
2

Find applicable taxes

Once you have the location codes for an employee’s home and work addresses, query the STE for a list of potentially applicable taxes. Each tax is identified by a Unique Tax ID.The engine also tells you whether any additional information about the employee or employer is needed to compute a tax. For example, federal income tax (FIT) can’t be calculated without first knowing the filing status the employee selected on their Form W-4.
Taxes returned by the STE are always “potentially applicable.” Special circumstances outside of what the STE tracks may make an employee or employer exempt. During setup you can exempt any tax as needed, or simply not set a tax up before calculating.
3

Calculate taxes

With the relevant location codes, tax IDs, and any required additional information in hand, you set up and compute the taxes for the employee and employer for the paycheck.During setup you also indicate any benefit contributions, imputed income, or other items that affect withholding. After running the calculation, retrieve the amount withheld for each tax and use those amounts in your system to determine the employee’s net pay.

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Two building blocks

The model rests on two fundamental concepts:

Location codes

Numerical representations of the overlapping jurisdictional boundaries that contain an address. They let the engine determine which taxes apply and which wages should be taxed.

Unique Tax IDs

A standardized identifier for every tax the STE supports. You tell the engine which taxes to calculate by their IDs, and results come back tied to the same IDs.

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Next steps

Once you’re comfortable with the model, learn how setup works in practice and run your first calculation.

Configure, then calculate

The setup-then-run workflow the STE uses for every calculation.

Quickstarts

Step-by-step guides for running your first payroll calculation.