FEMA flood zones explained

Checked against FEMA and other official sources · Last reviewed October 8, 2026

What a flood zone is

FloodSmart, the National Flood Insurance Program's (NFIP) official site, defines a flood zone as "a defined geographic area with a specific flood hazard risk." The zone is used to determine flood insurance requirements and costs.

Zones are drawn on a Flood Insurance Rate Map, or FIRM. Federal regulations define a FIRM as an official map of a community showing "both the special hazard areas and the risk premium zones applicable to the community." FEMA calls the flood map "the official source for determining flood risk within a community."

Most zones are measured against the base flood: the flood "having a one percent chance of being equalled or exceeded in any given year." FEMA says the 1-percent annual chance flood "is also referred to as the base flood or 100-year flood." See what a 100-year flood really means. [1][2][3][5]

High-risk zones: A zones (Special Flood Hazard Areas)

A Special Flood Hazard Area is land "subject to a 1 percent or greater chance of flooding in any given year." On the map, SFHAs are the zones that begin with A or V. FloodSmart says homes in these areas have "a 1 in 4 chance of flooding at least once" over a 30-year mortgage.

The A zones, with the meaning federal regulations give each one:

• Zone A: high-risk area "without water surface elevations determined," so no base flood elevation is shown. See flood zone A.
• Zone AE (and the numbered zones A1-A30): high-risk area "with water surface elevations determined." See flood zone AE.
• Zone AO: shallow flooding, with average depths of 1 to 3 feet, where there is no clearly defined channel and the flood path is unpredictable. See flood zone AO.
• Zone AH: shallow flooding of 1 to 3 feet, with water surface elevations determined. Federal rules describe shallow flooding in AO and AH zones as "ponding or sheet flow." See flood zone AH.
• Zone AR: an area behind a flood protection system, such as a levee, that was previously accredited but has been decertified. The system is being restored to give base-flood protection.
• Zone A99: an area where enough progress has been made on a protective system, "such as dikes, dams, and levees," to treat it as complete for insurance rating.

Areas with more than one hazard get combined labels, such as AR/AE or AR/AO. [1][5][6][7]

High-risk coastal zones: V, VE and V1-V30

V zones are SFHAs along the coast. FloodSmart says zones V and VE are "high risk coastal areas with an additional hazard from storm waves." The legal term is coastal high hazard area. It extends from offshore to the inland edge of the primary frontal dune along an open coast, plus "any other area subject to high velocity wave action from storms or seismic sources."

• Zone V: coastal high hazard area without water surface elevations determined.
• Zone VE (and the numbered zones V1-V30): coastal high hazard area with water surface elevations determined. See flood zone VE.

[3][5][6]

Moderate- and low-risk zones: B, C and X

FEMA calls areas outside the SFHA "Non-Special Flood Hazard Areas." These are the zones beginning with B, C or X. Some maps use B and C, and others use shaded and unshaded X for the same two categories:

• Zone B or shaded X (moderate risk): the area between the limits of the base flood and the 0.2-percent-annual-chance flood, also called the 500-year flood.
• Zone C or unshaded X (minimal risk): the area outside the SFHA and higher than the elevation of the 0.2-percent-annual-chance flood.

Lower risk is not zero risk. FloodSmart reports that from 2014 to 2024, "nearly one-third of NFIP flood insurance claims (29%)" came from areas outside the current high-risk flood areas. See flood zone X and flood zones B and C for details. [1][2][6][7]

Undetermined risk: zone D

Zone D is an "area of undetermined but possible, flood hazards." FloodSmart explains that no flood hazard analysis has been done there, so the risk is undetermined. FloodSmart says insurance rates there "are based on the uncertainty of the flood risk," and it recommends flood insurance. See flood zone D. [3][6]

When flood insurance is required

Federal law ties the requirement to the loan, not just the zone. Federally regulated lenders and federal agency lenders may not make, increase, extend or renew a loan on a building in a Special Flood Hazard Area without flood insurance, and Fannie Mae and Freddie Mac must have procedures to make sure the loans they buy are covered. This applies when NFIP insurance "has been made available" in that area. The coverage must be at least the outstanding loan balance or the maximum NFIP coverage for that type of property, whichever is less. Lenders must also accept private flood insurance that meets the requirements.

In FloodSmart's words: "You're required to have flood insurance if you own a home or business in a Special Flood Hazard Area (SFHA) and have a government-backed mortgage."

Outside the SFHA, flood insurance is "available, but not mandatory," according to FEMA. FloodSmart notes that "some banks require flood insurance even if you don't live in a high-risk area." Ask your lender about its terms. For the full picture, see do I need flood insurance?. [2][4][8]

Flood zones and what you pay

Your zone still decides whether the mandatory purchase rule applies. It no longer sets your NFIP premium by itself, though. FEMA says the NFIP's current pricing approach "does not use flood zones to determine flood risk." FloodSmart says flood zones and a building's elevation relative to the base flood elevation "are no longer the only factors" in setting premiums. See how much flood insurance costs. [3][9]

How to find and challenge your zone

FEMA calls its Map Service Center "the official public source for flood map." You can search it by address. Our guide to finding your flood zone walks through the steps.

Maps get updated over time, so FloodSmart suggests checking yours once a year. If you think your property was wrongly mapped into a high-risk zone, you can ask FEMA for a Letter of Map Amendment (LOMA) or a Letter of Map Revision. [2][3]

Questions people ask