Photo: Gensler

San Francisco financial technology company Credit Karma will expand to Oakland after signing one of the city’s largest office leases in the past few years.

The provider of free credit scores and other financial services leased 106,000 square feet at 1100 Broadway, a tower under construction next to the 12th Street BART Station.

Credit Karma, which has more than 1,000 employees, said the location will allow the company to grow, with another building that is easily accessible by BART from its headquarters at 760 Market St. in San Francisco, where it will remain.

Credit Karma is the second San Francisco tech company to sign major Oakland expansion plans in the past five months. In December, payments processing company Square leased 356,000 square feet at Uptown Station. Square will also keep its headquarters in San Francisco.

Oakland is benefiting from San Francisco’s dwindling supply of office space. Only one major office project under construction in San Francisco, Oceanwide Center, doesn’t have tenants. The city’s vacancy rate is below 5 percent.

“Square’s expansion into the market has strong potential to spur other tech tenants to migrate from San Francisco, where expansion opportunities are now limited,” brokerage Cushman & Wakefield said in a recent report. Oakland “is growing into a robust, mature office market where skilled employees desire to live as well as work.”

Downtown Oakland office asking rents have jumped 82 percent since 2012, and were $58.93 per square foot annually at the end of March, according to Cushman & Wakefield. That’s still about 30 percent below San Francisco’s downtown asking rents, which exceed $80 per square foot.

The 18-story 1100 Broadway project includes the renovation of the historic Key System Building, which has been vacant since the 1989 Loma Prieta earthquake. The new building is set to open early next year. The University of California Office of the President has leased 170,500 square feet in the building, leaving about 58,000 square feet of office space and 10,000 square feet of ground floor retail space still available.

Ellis Partners is the project developer, and Gensler is the architect.

Credit Karma said it doesn’t know how many employees it will house in the site, but the new location will enable it attract more workers from the East Bay. It currently has more than 60 job openings in San Francisco listed on its website. Founded in 2007, the company was valued at $4 billion last year and says it has over 85 million customers. Investors include Founders Fund, Ron Conway’s SV Angel, and CapitalG, previously called Google Capital.

The Registry, a real estate website, first reported the Credit Karma lease.

Oakland’s “access to transit, access to the city and surrounding region” is attracting more employers, said Edward Del Beccaro, East Bay regional manager at brokerage TRI Commercial. Many employees of San Francisco companies already live in the East Bay, which makes opening Oakland offices more attractive, he said.

Rising rents have led to the most office construction in a decade in Oakland. In addition to 1100 Broadway, new projects include developer Shorenstein’s 601 City Center office tower and Lane Partners’ 2150 Webster St. renovation.

In San Francisco, office projects are constrained by the city’s Proposition M office approval limits and lawsuits against the city’s new Central South of Market plan, which could delay the next wave of development.

Roland Li is a Chronicle staff writer. Email: roland.li@sfchronicle.com Twitter: @rolandlisf