Cost-of-living indexes explained: RPP, C2ER, and more
There are several cost-of-living indexes in circulation, and they are not interchangeable. Using the wrong one leads to incorrect salary calculations. This guide explains what each index measures and which one to use for different purposes.
Last updated June 2026
BLS Regional Price Parities (RPP)
RPPs are published annually by the Bureau of Economic Analysis. They measure the price level of an area relative to the U.S. average (set to 100) for a fixed basket of goods, services, and housing.
Coverage: All metropolitan statistical areas (MSAs) and states.
Methodology: Uses the same Consumer Expenditure Survey weights as CPI, applied to actual price surveys.
Lag: Typically 1-2 years behind present day.
Best for: Apples-to-apples salary and cost-of-living comparisons between any two U.S. metros.
ACCRA/C2ER Cost of Living Index
Published quarterly by the Council for Community and Economic Research, this index surveys prices in participating cities for a basket of items including groceries, housing, utilities, transportation, healthcare, and miscellaneous goods.
Coverage: Varies — typically 200-300 urban areas that voluntarily participate.
Methodology: Self-reported price surveys by local chambers of commerce.
Best for: Detailed category-level comparisons when both cities are well-covered.
Limitation: Participation bias — cities that participate tend to be larger or more research-oriented.
MIT Living Wage Calculator
This tool calculates the minimum wage needed to cover basic expenses by family type in any county or metro. It is not a cost-of-living index but rather a minimum-income benchmark.
Best for: Understanding poverty thresholds and minimum living standards.
Not for: Middle-income salary equivalency comparisons.
HUD Fair Market Rents (FMR)
Published annually by HUD, FMRs represent the 40th percentile of gross rents (rent + utilities) for standard quality housing in each metro area.
Coverage: All HUD-defined metro areas, including small markets.
Best for: Apartment budgeting and rental market benchmarking.
Limitation: Housing only — does not cover other cost-of-living categories.
Which index should you use?
- Total cost-of-living comparison: BLS RPP
- Rent budgeting: HUD Fair Market Rent
- Category-level detail (groceries, utilities, etc.): C2ER, if your cities are covered
- Minimum living wage: MIT Living Wage Calculator
ReloMath uses BLS RPP as the primary index and HUD FMR for rent benchmarks. Every data point is linked to its official source.
Frequently asked questions
What is the difference between RPP and the ACCRA/C2ER index?
The ACCRA/C2ER Cost of Living Index is based on quarterly surveys of prices paid by mid-management professionals in participating cities. Coverage is voluntary and varies by city. BLS RPP is based on comprehensive price surveys conducted by the federal government and covers all major metros consistently.
Why do different cost-of-living calculators give different results?
Different calculators use different underlying indexes, different base years, and different weighting methods. A calculator using C2ER data for one city and RPP data for another will give nonsensical results. Always use a single index consistently.
Is BLS RPP data free?
Yes. BLS RPP data is published by the Bureau of Economic Analysis (BEA) and is available free at bea.gov. ReloMath compiles it into a searchable database and verifies each entry against the official source.
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