On top of downloads and CDs, what the British public are streaming in the prestigious chart week will be included, the Official Charts Company said.
The rule change means festive classics from the likes of Mariah Carey and The Pogues could well join the 2014 Christmas number one race.
While a host of newer releases from Band Aid 30, The Peace Collective, Mark Ronson and The X Factor winner prepare to battle for the top spot, they face competition from festive classics that are being listened to by people using streaming services such as Spotify and Deezer.
While recent years have seen several vintage Christmas songs re-enter the top 40 thanks to the inclusion of digital downloads into the charts in 2005, the addition of streaming into the Official Singles Chart from July 2014 means they stand an even stronger chance at competing for a top 10 placing.
Already this year, Christmas songs and former Christmas number ones have been streamed 39 million times with 18.7 million streamed last week alone, OfficialCharts.com said.
The most popular is Mariah Carey's 1994 hit All I Want For Christmas Is You, which was streamed 861,000 times last week.
As Christmas party season gets into full swing and these classics are added to playlists up and down the country, Carey's seasonal tune could end up back inside the top 10 for the first time in seven years.
While making it all the way to number one might seem a stretch, its popularity on streaming services will propel the track harder than ever in that direction, the Official Charts Company said.
Since the inclusion of streaming data into the Official Chart this summer, number one singles have been racking up an average of 1.4 million streams in their chart-topping week.
The Pogues and Kirsty MacColl's Fairytale of New York has also seen a significant boost this year thanks to streaming.
The song, which was first released in 1987, is on track to enter the top 10 this weekend for the first time since 2007 and in addition to downloads was streamed 552,000 times last week.
Other popular Christmas songs that can expect a boost up the chart include Last Christmas by Wham!, which is set to re-enter the top 40 this week and was streamed 580,000 times in the last week alone.
And Wizzard's I Wish It Could Be Christmas Everyday is on course to re-enter the top 40 for its fourth consecutive year and was streamed 264,000 times last week.
The biggest-selling Christmas song this year is Band Aid 30's Do They Know It's Christmas?, which has sold almost 400,000 copies since its release on November 17.
The charity track is also expected to re-enter the top 10 this week following its physical release.
