MusicReasonScales, Keys, Intervals, and Notation
What does this interval invert to?
Choose an interval. This tool shows its inversion, the number and quality complement, and the semitone evidence behind the transformation, with an optional played demonstration.
Answer and Play
Want to learn more? Intervals: Number, Quality, Direction & Inversion
Understand
Inverting a simple interval always produces diatonic numbers that sum to nine and semitone sizes that sum to twelve, which is a fixed arithmetic fact, not a coincidence specific to any one interval. Perfect intervals stay perfect under inversion; major becomes minor and vice versa; augmented becomes diminished and vice versa.
Worked examples
A Major 3rd inverts to a minor 6th (3 + 6 = 9, 4 + 8 = 12). An Augmented 4th inverts to a diminished 5th (4 + 5 = 9, 6 + 6 = 12). A Perfect 5th inverts to a Perfect 4th, staying perfect on both sides of the inversion.
Method and limitations
A compound interval is reduced to its simple class before inversion, with that reduction shown rather than hidden, since inversion arithmetic is only defined cleanly for simple intervals. This tool does not attempt to invert a compound interval directly without that stated reduction step.
Where inversion actually gets used
Interval inversion shows up constantly in voice-leading and counterpoint reasoning: a melodic leap up a sixth and a leap down a third can be the same two notes viewed from different directions, and recognizing that relationship quickly is part of reading harmony fluently. It also explains why certain chord inversions and voicings share so many intervallic properties even though they look different on the page.