"You might be busy wishing everyone a Merry Christmas but may want to hold off a while before reaching out to your Russian friends. Like a few Christian Orthodox countries, Russians celebrate Christmas on the first week of January with celebrations taking on a slightly different look and feel to those of Western Europe.
Used by the Catholic and Protestant churches, the Gregorian calendar loses out to the Julian one, which the Russian Orthodox Church favors and which other Orthodox churches, such as the Greek one, use. And according to the Julian calendar Christmas usually falls on January 7th.
Following the 1917 Russian Revolution, when Bolsheviks banned Christmas and subdued Christian or Western imagery, Russia now views New Year’s Day as an analogous holiday with many of the same customs, such as decorating a fir tree and giving presents, incorporated into the day’s events. .....
... Unlike the U.K., Spain or other Western countries—when the head of state gives an annual speech on December 25—Russian President Vladimir Putin will be addressing the people on December 31 this year, as he does every year...." - read the rest of the article on the mentioned link.
December 25 is not a big a deal in Russia, as the party starts much later there.