“Guess” is a song by British artist Charli XCX, originally released on Brat and It’s the Same but There’s Three More Songs So It’s Not, the deluxe version of her sixth studio album Brat (2024). A remix featuring American singer-songwriter Billie Eilish was issued on 1 August 2024 as a single from Brat and It’s Completely Different but Also Still Brat, the album’s remix counterpart. Released alongside a music video that led to the donation of 10,000 pieces of underwear to I Support the Girls, the track marked Eilish’s first studio collaboration in several years and became the fourth remix released from the Brat era.

The song was met with widespread critical acclaim and achieved strong commercial success, reaching number one on the UK Singles Chart—Charli XCX’s first solo UK chart-topper. It also peaked at number twelve on the Billboard Hot 100 and topped the Billboard Hot Dance/Electronic Songs chart. Additionally, “Guess” reached number one in Australia, Ireland, Lithuania, and New Zealand, while placing within the top ten in Canada, Norway, and Sweden. The remix earned a nomination for Best Pop Duo/Group Performance at the 67th Annual Grammy Awards and won Song of the Year at the 2025 Brit Awards.