Data sources and method

Rules

• 26 U.S.C. 42, read on Cornell Law School’s Legal Information Institute (text including amendments through Public Law 119-21, July 4, 2025): (f)(1)-(2) credit period, (g)(1) and (g)(2)(D) set-asides and the next available unit rule, (h)(6)(D)-(I) extended use and qualified contracts, (i)(1) compliance period, (i)(7) right of first refusal, (j) recapture.
• 26 CFR 1.42-5 (compliance monitoring and record retention), 1.42-15 (available unit rule), 1.42-18 (qualified contracts, T.D. 9587, May 3, 2012), 1.42-19 (income averaging, T.D. 9967, October 12, 2022, as amended by a final rule of September 30, 2025 (FR Doc. 2025-19005)), from the eCFR.

Property data

HUD’s national Low-Income Housing Tax Credit database (LIHTCPUB, 55,345 projects placed in service 1987 to 2024, revised May 28, 2026), with HUD’s 2024 data dictionary, saved from huduser.gov on October 24, 2026. Credit type, the agency-reported affordability period (where longer than 30 years) and the no-longer-monitored flag come from the coded fields, decoded with that dictionary.

The tables keep projects placed in service from 2009 to 2018. The compliance-period year shown is the placed-in-service year plus 14, which assumes the owner started credits in the placed-in-service year. An owner can elect the next year (IRC 42(f)(1)), and buildings in one project can be placed in service in different years, so treat the year as a screen, not a fact about any one building. Extended use is shown as its statutory minimum, 15 years after the compliance period; many agreements run longer.

Refreshing

huduser.gov blocks scripted downloads, so LIHTCPUB.xlsx is saved by hand into data/raw/hud/; python3 scripts/build_data.py (needs python-calamine) rebuilds the tables.