spm-calculator 0.1.0

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 static web app that walks you through calculating your SPM threshold based on your household characteristics.

The calculator runs entirely in your browser with no server required - all data is pre-computed and bundled.

Run Locally

Static React 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

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 SPM three-parameter scale
• geoadj adjusts for local housing costs based on ACS median rents

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 geography
geoadj = calc.get_geoadj("congressional_district", "0612")  # CA-12
# 1.24 (24% above national average due to high housing costs)

# Calculate threshold for a specific family in a specific location
threshold = calc.calculate_threshold(
    num_adults=2,
    num_children=2,
    tenure="renter",
    geography_type="congressional_district",
    geography_id="0612"
)
# ~$48,893 (base $39,430 × equiv_scale 1.0 × geoadj 1.24)

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)

Following Census methodology:

GEOADJ = (local_median_rent / national_median_rent) × 0.492 + 0.508

Where 0.492 is the housing portion of the SPM threshold for renters.

Equivalence Scale

The SPM uses a three-parameter equivalence scale:

• First adult: 1.0
• Additional adults: 0.5 each
• Children: 0.3 each
• Normalized to reference family (2A2C = 1.0)

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

License

MIT License - see LICENSE for details.

Contributing

Contributions welcome! Please see CONTRIBUTING.md for guidelines.