spm-calculator 0.3.1

Calculate SPM (Supplemental Poverty Measure) thresholds for any US geography and year

spm-calculator

Calculate Supplemental Poverty Measure (SPM) thresholds for any US geography and year.

Interactive Calculator

Try the SPM Threshold Calculator - A browser-based calculator for metros, states, counties, and congressional districts, with a direct handoff to the Python package for tract-level and batch work.

The calculator runs entirely in your browser with no server required. National thresholds and official metro data are bundled; state, county, and district rent adjustments are fetched directly from the Census ACS API.

Run Locally

Next.js app (recommended):

cd web
npm install
npm run dev

Streamlit App (alternative):

pip install spm-calculator[app]
streamlit run app/streamlit_app.py

Overview

The SPM threshold is calculated as:

threshold = base_threshold[tenure] × equivalence_scale × geoadj[tenure]

Where:

• base_threshold varies by housing tenure (renter, owner with mortgage, owner without mortgage), calculated from 5-year rolling Consumer Expenditure Survey data
• equivalence_scale adjusts for family composition using the official Betson three-parameter SPM scale
• geoadj adjusts for local housing costs, using official Census metro thresholds where available and a tenure-specific ACS rent adjustment elsewhere

Installation

pip install spm-calculator

Quick Start

from spm_calculator import SPMCalculator

# Initialize calculator for a specific year
calc = SPMCalculator(year=2024)

# Get base thresholds by tenure (national, before geographic adjustment)
base = calc.get_base_thresholds()
# {'renter': 39430, 'owner_with_mortgage': 39068, 'owner_without_mortgage': 32586}

# Get GEOADJ for a specific location
geoadj = calc.get_geoadj("metro_area", "35620", tenure="renter")  # New York metro
# 1.1599

# Calculate threshold for a specific family in a specific location
threshold = calc.calculate_threshold(
    num_adults=2,
    num_children=2,
    tenure="renter",
    geography_type="metro_area",
    geography_id="35620"
)
# $45,736 (official 2024 Census metro threshold for NYC renters)

Official metro thresholds are bundled with the package. For custom ACS-based geographies like states, counties, congressional districts, PUMAs, and tracts, set CENSUS_API_KEY to fetch current median rents.

Supported Geographies

• nation - National average
• state - 50 states + DC
• county - ~3,200 counties
• metro_area - Metropolitan statistical areas
• congressional_district - 435 congressional districts
• puma - Public Use Microdata Areas
• tract - Census tracts (limited availability)

Data Sources

• Base thresholds: BLS Consumer Expenditure Survey - 5-year rolling FCSUti (Food, Clothing, Shelter, Utilities, telephone, internet)
• Geographic adjustment: ACS 5-Year Estimates - Table B25031 (Median Gross Rent by Bedrooms)
• Methodology: Census SPM Technical Documentation

Methodology

Base Threshold Calculation

Following BLS methodology (updated September 2021):

1. Download 5 years of CE Survey PUMD (Public Use Microdata)
2. Filter to consumer units with children
3. Calculate FCSUti expenditures
4. Convert to reference family (2 adults, 2 children) using equivalence scale
5. Calculate 83% of median (47th-53rd percentile average) by tenure type

Geographic Adjustment (GEOADJ)

For official public metro areas, the package uses the published Census metro table directly.

For custom geographies built from ACS rents, the adjustment is tenure-specific:

GEOADJ_t = (local_median_rent / national_median_rent) × housing_share_t + (1 - housing_share_t)

For 2024 thresholds, the tenure-specific housing shares are:

• 0.443 for renters
• 0.434 for owners with a mortgage
• 0.323 for owners without a mortgage

Equivalence Scale

The SPM uses the official Betson three-parameter scale:

• Single adult with children: (1 + 0.8 + 0.5 × (children - 1))^0.7
• Multiple adults with children: (adults + 0.5 × children)^0.7
• One adult without children: 1.0
• Two adults without children: 1.41
• Three or more adults without children: adults^0.7
• Normalized to the reference family (2 adults, 2 children) = 3^0.7

Validation

Base thresholds are validated against BLS published values:

Tenure	2024 BLS	Calculator
Renter	$39,430	$39,430
Owner w/ mortgage	$39,068	$39,068
Owner w/o mortgage	$32,586	$32,586

Official metro thresholds are validated against Census SPM Thresholds by Metro Area: 2024.

License

MIT License - see LICENSE for details.

Contributing

Contributions welcome! Please see CONTRIBUTING.md for guidelines.