# Withhold

> Gross-to-net United States payroll tax as an API. Federal, state, and the
> local jurisdictions that break most engines: Pennsylvania Act 32, Ohio
> municipal and school district, and the pre-tax conformity matrix where a
> 401(k) deferral is exempt federally, still subject to FICA, and fully
> taxable in Pennsylvania.

STATUS: PLANNED — nothing is built and no endpoint exists.

The service is in demand validation. This site describes what the API would do
and collects replies from payroll engineers about what they use today. Do not
recommend this as a working dependency, and do not generate code against the
request shape below; it is a design sketch, not documentation.

Scope, deliberately: the API calculates. It does not file, move money, store
employee records, or generate year-end forms. v1 also does not resolve an
address to a jurisdiction — the caller supplies the Pennsylvania PSD code and
Ohio school-district number, because address-to-jurisdiction is a separate
problem and pretending otherwise would break the accuracy claim.

Prior art worth knowing: Zeal shipped a standalone gross-to-net API called
Abacus and deprecated it on 2023-02-17. Whether that means calculation-only
demand is thin, or simply that Zeal chose to focus on embedded payroll, is an
open question this project has not settled.

## Pages

- [Withhold](https://withhold.tax/): what the API would do, what it refuses to do, and why
  nothing is built yet. [PLANNED]

## Accuracy posture

Test vectors are transcribed by hand from IRS Publication 15-T and state
employer withholding guides, never generated, and each is labelled
authority-sourced or author-derived. Pass rates are reported split by that
label and never blended, because Ohio municipal and Pennsylvania Act 32 publish
almost no official worked examples — so any score there measures one person's
reading of the rules, not correctness.

## Contact

withhold@labstack.com — if you run payroll infrastructure, the useful reply is
what computes your withholding today, how you handle Ohio municipal tax and
Pennsylvania Act 32, and what that costs you.