Square Inc. is aiming for a valuation of as much as $4.2 billion in its initial public offering, well short of the $6 billion the mobile-payments service sought in its latest funding round.

The large gap underscores a lingering question for the latest crop of startups: Will they be able to fetch the same rich valuations they are getting in private markets when they hawk their shares to public investors? The resounding “No” for Square is significant because it is one of the few young companies recently making the move to go public.

The company, founded and led by Twitter Inc. Chief Executive Officer Jack Dorsey, plans to market its shares at between $11 and $13 apiece, according to a regulatory filing Friday. The IPO will include about 27 million shares of the 323 million that will be outstanding after the offering. There is an option to set aside an additional 4 million shares to underwriters, meaning Square may seek to raise more than $400 million.

Square had been in talks for funding at a $6 billion valuation in August 2014, a person with knowledge of the matter said at the time.

Dorsey has said that Square co-founder Jim McKelvey came up with the idea for the company when he was trying to sell his art and found the process for setting up a merchant account “painful.” Square, which is mainly used by small businesses, uses a smartphone application that connects to a terminal.

Square, started in 2009 in San Francisco, is raising funds to generate working capital and may also use some of the proceeds to acquire complementary businesses and technology, the company said. Net revenue rose to $850.2 million last year from $552.4 million in 2013, Square said in the filing. Revenue was $892.8 million for the first nine months of this year.

Square warned that the revenue growth rate will probably decline and the company is unprofitable. The company’s net loss widened to $154.1 million last year from $104.5 million in 2013.

The company relies heavily on revenue from transactions in Starbucks Corp. stores. The coffee chain made up 17 percent of revenue last year. The partnership lost money for Square, which said it won’t renew its agreement when it expires next year.

At the midpoint of the offering range, Square would get net proceeds of $284.6 million from the sale, the company said. The stock will trade on the New York Stock Exchange under the ticker SQ. Goldman Sachs Group, Morgan Stanley and JPMorgan Chase & Co. are underwriting the IPO.

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