PolicyEngine Macro
model 01 — tax-benefit microsimulation · pe-microsim · UK · US · hosted
Exact for a household. Estimated for a country.
The working paper behind the suite’s lead model: what it computes, why household arithmetic carries no uncertainty and population estimates do, and what the macro bridge can and cannot supply.
Exact rules, estimated aggregates: the PolicyEngine tax–benefit microsimulation in an open model suite
Household arithmetic is exact and carries no uncertainty; a population estimate is a weighted sum of that arithmetic over an estimated population, and the paper refuses to blur the two. The single committed external benchmark is 1p on the UK basic rate: £6.46bn in 2026 against HMRC's June 2025 ready reckoner of £6.9bn in 2026–27, i.e. 6.4% below — and below at every year that can be matched. It is a benchmark, not a validation: the reckoner is post-behavioural on administrative SPI data where this costing is static on the enhanced FRS, so the two price different objects. No interval is reported for any population estimate, because the codebase does not produce one. Validation →
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Open the PDFSource & reproduction: papers/pe-microsim/ on GitHub · All papers →
Cite this work
Ahmadi, Vahid (2026). “Exact rules, estimated aggregates: the PolicyEngine tax–benefit microsimulation in an open model suite.” PolicyEngine Macro working paper. https://policyengine-macro.vercel.app/papers/pe-microsim
@techreport{policyengine2026pemicrosim,
title = {Exact rules, estimated aggregates: the PolicyEngine tax-benefit microsimulation in an open model suite},
author = {Ahmadi, Vahid},
year = {2026},
institution = {PolicyEngine},
url = {https://policyengine-macro.vercel.app/papers/pe-microsim},
note = {PolicyEngine Macro working paper}
}No DOI is assigned. For an exact version stamp, cite the git commit of the artifact you used from github.com/PolicyEngine/macro.