Computerworld reports that Microsoft lost money on its Surface tablets throughout its just-concluded 2014 fiscal year, adding hundreds of millions of dollars in red ink.

According to the 8-K statement filed with the U.S. Securities and Exchange Commission (SEC) on July 22, the Surface posted revenue of $409 million for the quarter that ended June 30. But unlike the two quarters prior, Microsoft did not reveal the cost of revenue associated with the Surface for the period.

Without a cost of revenue figure, it is impossible to calculate a precise gross margin, a rough measurement of profit. However, using information in the 10-K that Microsoft filed last Friday, along with data from earlier reports, it is possible to estimate Surface cost of revenue.

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