Data sources and method

QCT and DDA designations

• HUD’s 2027 lists, published in the Federal Register on October 6, 2026 (FR Doc. 2026-20390) and effective for allocations after December 31, 2026: QCT2027.csv (14,539 Qualified Census Tracts by 2020 census tract) and “2027 DDAs: Data Used to Designate” (2,657 metropolitan Small DDA ZCTAs and 286 nonmetropolitan DDA counties), from huduser.gov, saved October 24, 2026.
• HUD’s eGIS layers labeled “2026” were checked against those files and hold the same tracts and areas, so they are not used.
• Geocoding: U.S. Census Bureau geocoder, current benchmark, 2020 census tracts and ZCTAs.

Income and rent limits

HUD’s FY2026 Multifamily Tax Subsidy Project (MTSP) income limits (MTSP-Data-FY26.xlsx, and MTSP-IncAvg-Data-FY26.xlsx for the 20% to 80% income averaging levels; both files dated March 27, 2026), saved from huduser.gov October 24, 2026. One row per county, or per town in New England: 4,758 areas. Rents are computed the way IRS Publication 5913 (the Form 8823 Guide) shows: 30% of the income limit for the unit’s imputed household size (1 person for a studio, 1.5 per bedroom), averaging the two adjacent limits when the size isn’t a whole number, divided by 12 and rounded down to the dollar. Gross rent includes the utility allowance.

Apartment listings

HUD’s national LIHTC database, LIHTCPUB release revised May 28, 2026 (55,345 projects placed in service 1987 to 2024), with HUD’s 2024 data dictionary, saved from huduser.gov October 24, 2026. Cities with at least five properties get a page. Properties the allocating agency flagged as no longer monitored are left out.

Credit rules

• 26 U.S.C. 42(b), (c), (d)(5)(B), (f), (g), (h)(4), read on Cornell LII with amendments through Public Law 119-21 (July 4, 2025); Public Law 119-21 sec. 70422 from govinfo.gov.
• Rev. Rul. 2026-21 (November 2026 applicable percentages: 8.24% and 3.53%).
• Rev. Proc. 2025-32 sec. 4.08 and 4.19 (2026 state housing credit ceiling and private activity bond cap).
• Rev. Rul. 2020-4 (income averaging levels as multiples of the very low-income limit).
• HUD’s 2027 QCT and DDA notice (FR Doc. 2026-20390, October 6, 2026), for definitions and effective-date rules.

Refreshing

huduser.gov blocks scripted downloads, so the HUD files are saved by hand into data/raw/hud/ (zip files unpacked into data/raw/hud_unz/). python3 scripts/build_data.py (needs python-calamine) rebuilds the JSON the pages use.