In music, the subtonic is the lowered seventh degree of the scale, as opposed to the leading tone. For example, in the A minor scale (white keys on a piano), the subtonic is the note G (in C this would be Bb); and the subtonic chord uses the notes G, B, and D (in C: BbDF). In music theory, the subtonic chord is symbolized with the Roman numeral VII if major or vii if minor.

"Subtonic" also refers to a relationship of musical keys. For example, relative to the key of C major, the key of Bb major is the subtonic. Modulation (changes of key) to the subtonic are relatively rare, compared with, say, modulation into the dominant.