Time Warner is struggling to expand HBO Now, the cable-free streaming service of the popular premium pay-TV network, The Post has learned.

While HBO brass had set its sights on a good chunk of the estimated 15 million homes that have cut the cable cord, HBO Now’s subscriber count currently hovers “just above 1 million,” one source familiar with the service said.

That’s up just slightly from March, when HBO said it was nearing the 1 million mark. As of last Dec. 31, there were 800,000 subscribers.

Insiders point to the possibility that millennials aren’t rushing to the 20-month-old service, in part because mock news fave Jon Stewart has yet to debut an animated online-only news show.

Meanwhile, sports writer Bill Simmons’ “Any Given Wednesday” failed to arouse interest and was axed.

Distribution isn’t a problem for the $14.99 a month service.

While it started only on Apple TV, HBO Now is now available in Sony’s PlayStation, Microsoft’s Xbox and, beginning last week, on a paid tier alongside Amazon Prime Video’s channels.

HBO also said it would be available for $5 per month as part of DirecTV Now, owned by AT&T, which is in the process of buying Time Warner.

An HBO spokesman said owner Time Warner would likely update overall subscriber counts as part of its fiscal fourth-quarter and full-year earnings report, which usually occur in February.

Competitors include CBS’ Showtime, which also has 1 million subscribers, and Liberty Media’s Starz and Epix (owned by Paramount, MGM and Lionsgate).

While HBO Now’s stunted growth may seem disappointing, HBO is still a hugely lucrative profit driver for Time Warner, with the vast bulk of its revenue still derived from the pay-TV industry.