---
title: "PolicyEngine US"
subtitle: "Methodology and reference for the US tax-benefit microsimulation model"
---

PolicyEngine US is an open-source microsimulation model of the US tax and benefit system. It combines statutory rules encoded as Python formulas with a calibrated microdata foundation to answer policy questions at the household, state, and national level.

This site covers:

- **[Methodology](methodology/index.qmd)** — how the model is built: rules, data, calibration, and decompositions like medical out-of-pocket expenses.
- **[Programs](programs/index.qmd)** — program-by-program writeups that trace eligibility, benefit value, and household-paid costs.
- **[Reference](reference/index.qmd)** — auto-generated variable catalog pulled from the model's metadata API.

The underlying code lives at [github.com/PolicyEngine/policyengine-us](https://github.com/PolicyEngine/policyengine-us). Every page here is reproducible — code blocks run against the installed model version when the site is built, so numeric results track the release rather than being pinned to whenever prose was written.
