> ## Documentation Index
> Fetch the complete documentation index at: https://docs.symmetry.com/llms.txt
> Use this file to discover all available pages before exploring further.

# How calculators work

> A CBS calculator is one REST resource and one widget running the same gross-to-net calculation.

Every CBS calculator is the same thing exposed two ways, a **REST resource** and a **widget**, both running the **same calculation**.

## One calculator, two front doors

* **REST resource**, each calculator is an endpoint under `/api/calculators/<calculator>` (for example `/api/calculators/salary`). A `GET` returns the calculator's field model; a `POST` runs a calculation.
* **Widget**: the hosted widget for that calculator renders a UI and, under the hood, calls that same REST endpoint with your key.

Because both paths run the same calculator, the inputs and results are identical whichever you use. For the list of calculators and which paths support each, see [Available calculators](/cbs/overview/available-calcs).

## The gross-to-net calculation

A calculator takes wages, jurisdictions, and filing details and computes federal, state, and local withholding plus payroll taxes. Each one decides which inputs to collect and which method to apply, then returns the result through the widget or the REST endpoint.

<Note>
  Symmetry maintains the tax rules behind the calculators, so results stay current with tax changes without any work on your side.
</Note>

## From inputs to results

<Steps>
  <Step title="Collect inputs">
    Wages or rates, pay frequency, filing status, work and resident jurisdictions, and any calculator-specific fields (bonus amount, contribution percentage, and so on).
  </Step>

  <Step title="Apply the calculation method">
    Each calculator uses a specific withholding method: annualized, flat (supplemental), or current aggregation. See [Calculation methods by calculator](/cbs/core-concepts/calc-methods).
  </Step>

  <Step title="Run the calculation">
    The calculator computes federal, state, and local withholding plus Social Security and Medicare.
  </Step>

  <Step title="Return results">
    Gross pay, itemized taxes, deductions, and net pay, ready to display, store, or report on. See [Request and response structure](/cbs/api/request-and-response).
  </Step>
</Steps>

<Note>
  The same wages can produce different taxes and net pay across calculators, because each calculator uses a different method. This is expected.
</Note>