A family of four with an annual income of $84,450 or less now qualifies as low income in Orange County.

A single person living alone qualifies as low income if he or she earns $58,450 or less a year.

Orange County has the fifth-highest income threshold in the nation, according to new income limits released last month by the U.S. Department of Housing and Urban Development.

Government and private agencies use HUD’s income calculations to determine eligibility for a wide variety of assistance programs, ranging from rent subsidy vouchers and public housing to mortgage assistance. While low-income families qualify for some programs, others are limited to households earning far less, with limits as low as $31,300 for a family of four.

Record-high rents and home prices are driving up Southern California income limits. Orange County apartment rents, for example, increased 20 percent over the past seven years, while the median sale price of an Orange County house has jumped 40 percent.

“When you tell somebody that’s making $70,000 that they’re low income, they go, ‘What? That’s low income?’ Unfortunately, that’s what comes from living in a high-cost county,” said Cesar Covarrubias, executive director of the Kennedy Commission, an Irvine-based affordable housing advocacy group. “That makes it difficult for working families at all levels.”

Under the 2017 figures, Orange County’s income threshold for a family of four jumped $5,450 from last year’s level. The only metro areas with higher income limits are San Francisco; Fairfield County, Connecticut; Silicon Valley and Honolulu.

Even a six-figure salary doesn’t cut the mustard in San Francisco, Marin and San Mateo counties. A family of four there earning $105,350 or less now is considered low income, HUD figures show.

Orange County income limits for a family of four exceed Philadelphia’s ($66,550), Seattle’s ($72,000), Los Angeles County’s ($72,100), San Diego’s ($72,750) and Boston’s ($78,150).

Even New York City and east Long Island (which includes the Hamptons) have lower limits: $76,300 for a family of four in the Big Apple and $81,000 in Nassau and Suffolk counties.

The income limit for an Inland Empire family of four increased $500 this year to $51,600.

A family qualifies as low income if it earns roughly 80 percent or less than the median income for a given metro area, although adjustments are made to reflect a high-cost area’s rent and home prices.

HUD listed Orange County’s median income at $88,000 this year, Los Angeles County’s at $64,300 and the Inland Empire’s at $63,200. Bay Area median incomes are even higher: $115,300 for the San Francisco area, $113,300 for Silicon Valley and $97,400 for the East Bay’s Alameda and Contra Costa counties.

The low-income threshold shouldn’t be confused, however, with even lower income limits that qualify residents for various programs for the poor, such as new Section 8 rent vouchers or public housing.

For example, 75 percent of new admissions to the Section 8 rental assistance program must have incomes at roughly 30 percent or below an area median income. For a family of four, that “extremely low income” category is limited to those earning no more than $31,300 a year in Orange County, $27,050 in Los Angeles County and $24,600 a year in the Inland Empire.

But other programs are available to families in the “low-income” category. For example, NeighborWorks Orange County’s CalHome program provides down-payment assistance and second mortgages to low-income homebuyers.

High-income limits are justified in a county where the median house price tops $700,000, said Karla Lopez del Rio, NeighborWorks’ vice president of marketing.

“You probably need to make three times the median income to afford the median-priced house,” Lopez del Rio said. “Actually (the income limit) is not high enough for our reality.”

In addition to federal programs, a number of local, state or private agencies base their own income qualifications on HUD limits.

For example, private affordable housing projects built with federal low-income tax credits rely on the HUD data for determining resident eligibility, as do nonprofit groups providing down-payment assistance or low-cost mortgages.

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