Cities in the Pacific time zone have the least-affordable housing in the country, and the Central time zone has the most-affordable housing.

Each quarter, NerdWallet calculates the home affordability for 178 metropolitan areas, matching the list of metros for which the National Association of Realtors publishes median home prices. This quarter, NerdWallet sorted the metro areas by time zone, highlighting differences in affordability.

NerdWallet compared median household incomes and median home prices, assuming a 20 percent down payment. A place with high incomes and low home prices is more affordable for buying a home than an area with low incomes and high home prices.

Here are the most and least affordable metro areas in each time zone of the contiguous U.S. in the fourth quarter of 2018, compiled using data from the National Association of Realtors, the U.S. Census Bureau and NerdWallet surveys. (Honolulu, two time zones farther west, has the second-least-affordable homes in the country. NAR's quarterly price survey doesn't include cities in Alaska.)

PACIFIC TIME ZONE

MOST AFFORDABLE: KENNEWICK-RICHLAND, WASHINGTON

Median home price: $278,400 (national median price: $257,600)

Median household income: $63,617

Principal and interest payment: $1,183 (22.3 percent of median monthly income)

In Kennewick-Richland, a median-income household buying a median-priced house and putting 20 percent down pays 22.3 percent of that income on the mortgage's principal and interest. That's roughly the same share of income as the least affordable housing market in the Central time zone.

LEAST AFFORDABLE: SAN JOSE-SUNNYVALE-SANTA CLARA, CALIFORNIA

Median home price: $1.25 million

Median household income: $117,474

Principal and interest payment: $5,313 (54.3 percent of monthly income)

Here, in the country's most expensive metro area, a buyer of a typical home would get a $1 million mortgage after a 20 percent down payment.

MOUNTAIN TIME ZONE

MOST AFFORDABLE: EL PASO, TEXAS

Median home price: $157,900

Median household income: $44,416

Principal and interest payment: $671 (18.1 percent of monthly income)

While most of Texas is in the Central time zone, El Paso is so far west that it's in the Mountain zone. The median household income is modest, but so are home prices.

LEAST AFFORDABLE: BOULDER, COLORADO

Median home price: $592,300

Median household income: $80,834

Principal and interest payment: $2,518 (37.4 percent of monthly income)

Boulder has been called "the most expensive non-resort town in Colorado," and the city's leaders have been searching for ways to make housing affordable for middle-income households.

CENTRAL TIME ZONE

MOST AFFORDABLE: DECATUR, ILLINOIS

Median home price: $89,300

Median household income: $51,970

Principal and interest payment: $380 (8.8 percent of monthly income)

This central Illinois city had the lowest median house price among the 178 metro areas that NAR tracks.

LEAST AFFORDABLE: SHREVEPORT-BOSSIER CITY, LOUISIANA

Median home price: $170,100

Median household income: $38,627

Principal and interest payment: $723 (22.5 percent of monthly income)

In this metro area in northwestern Louisiana, a typical home costs about $87,000 less than the median home in the United States . But the median household income is low, too, making it difficult to afford a house.

EASTERN TIME ZONE

MOST AFFORDABLE: YOUNGSTOWN-WARREN-BOARDMAN, OHIO-PENNSYLVANIA

Median home price: $97,200

Median household income: $45,382

Principal and interest payment: $413 (10.9 percent of monthly income)

The Youngstown metro area had the second-lowest prices tracked by NAR. Its population is shrinking, which can suppress housing demand and keep prices low.

LEAST AFFORDABLE: NAPLES-IMMOKALEE-MARCO ISLAND, FLORIDA

Median home price: $432,800

Median household income: $66,048

Principal and interest payment: $1,840 (33.4 percent of monthly income)

This metro area had the second-highest income inequality in the U.S. in 2015, according to a 2018 Economic Policy Institute report. Collier County voters approved the county's first-ever sales tax in November, which earmarks some money for workforce housing.

HOW NERDWALLET CRUNCHED THE DATA

Affordability was estimated by comparing each metro area's median annual household income with the monthly principal-and-interest payment for a median-priced single-family home in the fourth quarter of 2018. (Median means half the incomes and prices are higher.) After a 20 percent down payment, house payments were calculated at an interest rate of 4.91 percent , the average rate for a 30-year fixed-rate mortgage in the fourth quarter in NerdWallet's daily mortgage rates survey. Payments exclude insurance and property taxes.

Metro-area median household income is from the U.S. Census American Community Survey of 2017. Median prices for resales of existing single-family homes in the fourth quarter came from the National Association of Realtors.

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This article was provided to The Associated Press by the personal finance website NerdWallet. Holden Lewis is a writer at NerdWallet. Email: hlewis@nerdwallet.com. Twitter: @HoldenL.

RELATED LINKS:

NerdWallet: Tips for first-time home buyers http://bit.ly/nerdwallet-tips-first-time-home-buyers