Swift, who reached the milestone last weekend, performed at New York City's Jingle Ball before carrying on the party at her apartment in Tribeca.
Alongside a photo of her posing with the 'Drunk in Love' hitmakers and Justin Timberlake, Sam Smith, Karlie Kloss and girl band HAIM, she wrote, "So this is being 25... #WHAT #bestbirthdayEVER. (sic)"
Swift was also joined at the party by Emma Roberts, Ansel Elgort, Kelly Osbourne, Nick Jonas and Chrissy Teigen as well as best friend Selena Gomez.
The singer shared a snap of her newly-manicured nails, which were decorated with two halves of a heart, each with a letter in: S and T.