Netflix is adding almost as many subscribers in one year as HBO did in 40 years

  • Barclays says Netflix's subscriber growth is "incredible."
  • Netflix is on pace to add 27.4 million subscribers this year, a new record for the company.
  • The year-over-year increase in subscribers is "the key to sustaining valuation," Barclays said.

Barclays estimated Netflix is on pace to add 27.4 million global subscribers this year — an "incredible" rate of subscriber growth the firm said is nearly as many as HBO has added in the U.S. across the last 40 years.

Netflix has nearly matched last year's total subscribers added in three fewer months, Barclays noted, putting the online streaming service on track to set a new record this year. Not including Cinemax, HBO had around 30 million U.S. subscribers as of 2014, according to Barclays, a little more than 40 years after its start. HBO was founded in 1972 but first gained national distribution via satellite in 1975.

The firm's comparison gives a better understanding of how quickly Netflix is expanding both in the U.S. and abroad.

The year-over-year increase in subscribers is "the key to sustaining valuation," Barclays said in the note to clients Wednesday. Netflix crushed Wall Street's expectation for subscriber growth when the company reported third-quarter earningsafter the bell on Tuesday.

"Given the miss last quarter, there was understandable worry going into earnings especially around" how many subscribers Netflix would add in the fourth quarter, Barclays said. "Any doubt about [Netflix's] momentum should be assuaged given the guide."

The company is projecting it will add 9.4 million net subscribers during the fourth quarter. "We're getting a little better on the forecasting," CEO Reed Hastings said after the earnings report. "I think by focusing going forward on paid [net adds] we'll be able to be a little more accurate and focus on the fundamentals."

Netflix rose 4.7 percent in trading to $362.88 a share. The stock has skyrocketed over the past 12 months, up 73.7 percent before Tuesday's earnings report.

— CNBC's Michelle Castillo contributed to this report.