By having its subscribers pay an average of about $8 a month to rent their cable modems rather than buy them, Comcast (Nasdaq: CMCSA) makes more in one quarter off modem rentals than it generated from the entire Sochi Winter Olympics.

That's the creative conclusion of Ken Kam, president and CEO of San Fancisco-based investment-management firm Marketocracy, who explains his detailed accounting in Forbes.

Through informal surveys and discussions with Comcast employees, Kam estimates that over 90 percent of Comcast's 21.3 million broadband and 11 million voice customers rent Arris-made modems from the conglomerate, each paying an average of around $8 a month.

"After crunching the numbers it looks like renting cable modems contributes between $275 million and $300 million per quarter to Comcast's bottom line," Kam concludes. The Sochi Games, by comparison, generated $257 million in revenue for the conglomerate in the first quarter.

Of course, Comcast rents out cable set-tops for its video subscribers. But Kam says he's specifically interested in cable modems because this is hardware Comcast consumers could buy inexpensively at retail … and save a lot of money in doing so.

What is the risk to Comcast if consumer behavior suddenly shifted and subscribers ventured en masse to Amazon to buy their modems instead?

"Putting it all together, the business of renting cable modems is worth between $3.8 billion and $5.8 billion to Comcast's shareholders," Kam writes. "It's a lot of money, but Comcast's market cap is north of $140 billion, so the risk to Comcast stockholders of people buying their own cable modems en-masse is not as big as I thought it might be."

Comcast has not yet responded to FierceCable's query for comment.

For more:

- read this Forbes post

Related links:

Comcast banks on rate hikes, cable modems, voice service to counter increased programming cost

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