The incident occured on the final lap of the Spanish race as Magnussen, on a three-stop strategy and on relatively fresh soft-compund tyres, was hounding Palmer - two-stopping and on old hards - in a fight for 13th place.
The pair made contact at Turn 13, for which the stewards blamed Magnussen. As it happened on the final lap, the Dane had 10 seconds added on to his race time, dropping him from 14th to 15th in the final results, behind Sauber's Felipe Nasr.
A statement from the stewards read: "Car 20 [Magnussen] was on a new set of soft tyres, and Car 30 [Palmer] was on an older set of hard tyres leading the driver of Car 20 to have significantly better grip and speed.
"However, the Stewards determined that Car 20 could not have reasonably expected to make the corner of Turn 13 without colliding with Car 30, which was subsequently forced off the track. The Stewards imposed the penalty referred to, which was converted to a time penalty after the race as the cars were on the last lap."
In addition Magnussen was given two penalty points on his licence - his first two of the maximum 12 permitted.
"It wasn’t a good day for me and I’ll be working closely with the team to understand why we weren’t able to deliver," Magnussen said following the race.
