How much will you pay for your next apartment?

With Rentberry, that all depends — on how much you’re willing to bid. The new real estate website is shaking up the Bay Area’s housing market by encouraging potential renters to bid on homes the way they would on designer handbags or celebrity autographs on Ebay.

Some housing advocates worry that Rentberry — and similar Vancouver-based startup Biddwell, which is set to expand to California by the end of the year — could intensify the existing competition for Silicon Valley’s few available houses and apartments. Critics envision the websites spurring cutthroat bidding wars that will drive sky-high prices even higher, but the platform’s founders say their tenants are actually saving money.

“It’s not about increasing prices,” said Alex Lubinsky, co-founder and CEO of San Francisco-based Rentberry. “It’s all about knowing and controlling the situation.”

But Rentberry’s impact on the Bay Area market may be particularly significant, as buying a home becomes an increasingly unattainable goal for many, and more people choose to rent. The proportion of local renters is up about 5 percent compared to 10 years ago, according to a report by New York University’s Furman Center for Real Estate and Urban Policy.

On the Rentberry website, landlords post photos of their properties, along with the desired monthly rent, and potential tenants then compete openly with each other to float the best offer. The site tells prospective tenants how many other applicants are in the running for each home or apartment, lists the highest offer received so far, and suggests a higher bid. Tenants also bid on a security deposit.

The site launched last year in San Francisco, Los Angeles and New York, and expanded its reach nationwide in April. Tenants pay $9.99 each time they submit an application for housing, and landlords who have more than two properties on the site pay $24 per month. So far, landlords have listed nearly a quarter of a million properties on the platform.

For some housing advocates, who are watching with dismay as ever-rising rents squeeze tenants throughout the Bay Area, Rentberry raises alarm bells. The median rent for a two-bedroom apartment in San Jose was $2,566 in October — up almost 22 percent from January 2014, according to Apartment List. Rent in San Francisco rose by 21 percent during that time period, and in Oakland it climbed 16 percent.

“I think that it’s unfortunate,” Sophia DeWitt, program director for East Bay Housing Organizations, said of Rentberry’s business model, “because any site or option like this that is going to increase or strengthen the speculative market in housing is bad for rental prices. That will just increase the rental prices, and it’s bad for renters.”

But Lubinsky swears his platform isn’t raising rents — in fact, it’s doing the opposite, because landlords are not automatically handing the lease to the highest bidder. It’s difficult and costly to evict a bad tenant, so most landlords would rather find a tenant who will stay for years and pay the rent on time, instead of a tenant who signs a lease for more money but stops paying after a few months, Lubinsky said. To do that, Rentberry landlords evaluate a potential tenant’s credit score, renter profile and other qualifications. And tenants can see each other’s information (anonymized to protect privacy), and get a clearer picture of where they stand in the competition.

On average, tenants using Rentberry pay between 4 and 6 percent below the landlord’s asking price, Lubinsky said — even in the Bay Area. When the site first launched last year, he told the San Francisco Chronicle that landlords could expect to see rental income increase an average of 5 percent. But that original estimate was based on an early beta test of just 10 landlords, he said, and did not end up becoming a larger trend.

Greg Rempe says using Rentberry saved him money. The 23-year-old moved from New Mexico to San Jose in June for a job at a startup, and stumbled upon Rentberry while searching for apartments on Google.

He bid on three apartments, but was determined not to enter a bidding war. For each apartment, he chose a maximum price that he wasn’t willing to exceed. One of the landlords ended up accepting his offer of $2,000 a month for a one-bedroom — below the $2,100 asking price, and below some of the other bids. It was more than he was used to paying in New Mexico, but Rempe walked away feeling like he got a good deal.

“I’m assuming it’s because I have a good credit score, but I don’t really know,” Rempe said. “Maybe I got lucky.”

Rempe appreciated the transparency of the bidding process. It was nice to know immediately where he stood in relation to a landlord’s other offers, he said. And after he moved into his new apartment Rempe used Rentberry to set up automatic payments for his rent, meaning he didn’t have to go through the hassle of sending his landlord a check every month.

Rentberry isn’t the only real estate platform that lets tenants bid on their rent. Biddwell operates with a similar model, but with one key distinction — bidding is done confidentially, so prospective tenants can’t see competing offers and try to one-up each other.

“We consciously make an effort to protect against bidding wars,” said co-founder and CEO Jordan Lewis, who helped launch the company in late 2016. “We want to use it more as a tool to facilitate negotiation.”

But that wasn’t always the case. When Biddwell launched the first test version of its platform, it looked more like Rentberry — it used an open system where potential tenants could see and respond to each other’s bids. That bidding process quickly began driving up rents, so Lewis’ team changed their game plan, and hid the bids. Potential tenants now see how many people have made an offer on a property, and if those offers are coming in at, above or below the asking price, but they can’t see individual bids.

As a result, 64 percent of offers accepted on the platform are below the landlord’s asking price, Lewis said.

Matt Regan, senior vice president of public policy for the Bay Area Council, said he isn’t worried about companies like Rentberry and Biddwell wreaking havoc on the local housing market. That’s mostly because the situation is already so bad that these platforms likely can’t do much to make it worse. In fact, he said, the Bay Area’s dire housing shortage means prospective tenants already engage in apartment bidding wars every day.

“This is probably a storm in a teacup,” Regan said, “compared with the tempest that’s swirling around us.”