Data · Methodology · Version 1
How the Flood Insurance Cost Index Is Built
Every figure in the Out of the Storm News Flood Insurance Cost Index traces to a public federal dataset, a stated formula, and a stated time window. This page documents the source, the exact metric definition, how we aggregate it, when it updates, and what it cannot tell you.
Latest data period: · Snapshot generated
Source data
The index is computed from FEMA OpenFEMA NFIP policy transaction data (FimaNfipPolicies), FEMA’s public record of individual NFIP policy transactions. Each record represents one policy that became effective — newly written or renewed — with its premium, total charge (premium plus fees and surcharges), effective date, state, and county FIPS code. We use no proprietary or private-market data.
Exact metric definition
The metric: Average premium among policies newly written or renewed that month (NFIP transactions) — not the official in-force average.
Transactions are grouped by the calendar month of their policy effective date (transaction-month aggregation). Within each month and geography, averages are weighted by policy count — every policy transaction counts once, so a county with 5,000 renewals influences its state average 5,000 times more than a county with one.
Formulas
- Average premium (geography, month) = sum of policy premiums for transactions effective that month in that geography ÷ number of those transactions.
- Average total cost = the same calculation using the policyholder’s total charge (premium + federal policy fee + surcharges + assessments).
- National average = policy-count-weighted average across all reporting states for the month (equivalently, the sum of all premiums nationwide ÷ all transactions nationwide).
- Year-over-year change = (latest month ÷ same month one year earlier − 1) × 100. Where a state lacks the 12-months-prior period, we compare against the earliest available month and label the change “since <month>” instead of “year over year.”
- vs. national = (state average ÷ national average − 1) × 100, both for the latest period.
Update cadence and data lag
We refresh the snapshot monthly, after FEMA publishes a new complete month of transactions. OpenFEMA transaction data is published on a lag of roughly two months; the latest period shown reflects that lag. In practice the newest period shown is about two months behind the calendar (M-2): the May 2026 period is the latest complete month available as of this snapshot.
Limitations — read before citing
- Not the in-force average. These are averages of the policies transacted each month, not of all active policies. FEMA’s official in-force statistics will differ, sometimes substantially.
- Monthly mix effects. The blend of properties renewing shifts month to month (coastal vs. inland, legacy-rated vs. Risk Rating 2.0 pricing), so part of any monthly move is composition, not price change for a fixed home.
- Small-sample noise. Counties and small states with few transactions produce volatile averages; check the policy-count column before drawing conclusions.
- NFIP only. Private flood insurance is excluded entirely.
- Unmatched reporting areas. A small number of records carry rollup or nonstandard FIPS codes; these appear in county tables under their raw FIPS code rather than a county name.
Frequently asked questions
Is this the official average cost of flood insurance?
No. The index reports the average premium among policies newly written or renewed in a given month (NFIP transactions). FEMA's official in-force averages describe every active policy at a point in time; our figures describe the policies that started or renewed that month, which makes them a faster-moving cost-trend signal but not a substitute for the official statistic.
Where does the data come from?
Every number is computed from FEMA OpenFEMA NFIP policy transaction data (FimaNfipPolicies), FEMA's public record of NFIP policy transactions, available at https://www.fema.gov/openfema-data-page/fima-nfip-policies-v2. We do not use proprietary or private-market data in this index.
Why is the latest month about two months old?
OpenFEMA transaction data is published on a lag of roughly two months; the latest period shown reflects that lag. We publish the newest complete month once it appears in OpenFEMA, which is why the index runs on an M-2 schedule rather than showing the current calendar month.
Why do monthly averages jump around in small states?
The average in any month reflects only the policies written or renewed that month. In states or counties with few transactions, a handful of unusually priced policies — for example, a batch of high-value coastal renewals — can move the monthly average noticeably. Policy counts are shown next to every average so you can judge how sturdy each figure is.
Does the index include private flood insurance?
No. The NFIP transaction file covers only National Flood Insurance Program policies. Private-market flood policies, which are a growing share of some coastal states, are not represented.
Can I reuse these figures or the CSV files?
Yes. The tables and CSV downloads are free to reuse with attribution to Out of the Storm News and a link to the page you drew from. A suggested citation appears in the “Use this data” block on every data page.
Changelog
- v1 — July 2026. Initial release: national trend, 53 state pages with county breakdowns, 13 monthly periods through May 2026, CSV downloads, and this methodology.
Corrections
If you find a figure that does not reconcile with the OpenFEMA source, email corrections@outofthestormnews.com with the page URL and the period in question. Confirmed errors are corrected in the next snapshot and noted in the changelog above.