In terms of chords and melody, 12 Days of Christmas has complexity on par with the typical song, having near-average scores in Chord Complexity and Chord-Bass Melody and below-average scores in Melodic Complexity, Chord-Melody Tension and Chord Progression Novelty.
12 Days of Christmas is written in the key of F Major. According to the Theorytab database, it is the 6th most popular key among Major keys and the 6th most popular among all keys. Major keys, along with minor keys, are a common choice for popular songs. The three most important chords, built off the 1st, 4th and 5th scale degrees are all major chords (F Major, B♭ Major, and C Major). See the F Major Cheat Sheet for popular chords, chord progressions, downloadable midi files and more!