A half-diminished chord, written m7b5, is a four-note chord built from a root, a minor 3rd, a diminished 5th and a minor 7th. Am7b5 is A, C, Eb and G (spelled A, C, D# and G), and it is the ii chord of a minor key.
What is a half-diminished chord?
A half-diminished chord, written m7b5, is a diminished triad with a minor 7th added on top. Am7b5 is A, C, Eb and G, spelled A, C, D# and G in ChordFlow's sharp-only system: the root, the minor 3rd three semitones up, the diminished 5th six semitones up, and the minor 7th ten semitones up. The name half-diminished comes from the fact that only half of the chord is diminished: the triad is fully diminished, but the 7th is minor rather than diminished, so the chord is halfway between a diminished 7th chord and a minor 7th chord. Half-diminished chords are the ii chord of every minor key, which makes them essential in jazz and in any minor-key music with a ii–V–i progression. In A minor the ii chord is Bm7b5, B, D, F and A, and it leads naturally to E7, the V chord, and then home to Am. The chord sounds tense and dark, but less harsh than a fully diminished 7th chord, because the minor 7th softens the top of the chord. Jazz musicians love it for exactly that reason: it has enough tension to move the harmony forward without sounding alarming.
How half-diminished chords are built
Build the diminished triad first, then add the minor 7th. For Bm7b5: B diminished is B, D and F, and the minor 7th above B is A, ten semitones up, so Bm7b5 is B, D, F and A. For Dm7b5: D diminished is D, F and Ab, spelled D, F and G#, and the minor 7th above D is C, so Dm7b5 is D, F, G# and C. For Cm7b5: C diminished is C, Eb and Gb, spelled C, D# and F#, and the minor 7th above C is Bb, spelled A#, so Cm7b5 is C, D#, F# and A#. The chord contains a tritone between the root and the diminished 5th, B to F in Bm7b5, which is what creates its pull toward the dominant. But it also contains a minor 7th that softens the sound: compare Bm7b5 with Bdim7, B, D, F and Ab, where the diminished 7th, Ab, makes the chord fully symmetrical and much harsher. The half-diminished chord keeps one foot in the minor world and one in the diminished world, and that is why it works so well as a ii chord: it is tense enough to move, but smooth enough to sit in a progression. The Bm7b5 guitar chord and the Am7b5 guitar chord show the shapes, and the key of A minor shows where Bm7b5 belongs.
Worked example — Dm7b5 in C minor. In C natural minor the ii chord is Dm7b5: D, F, Ab and C, spelled D, F, G# and C. It leads to G7, the V chord of C minor, and then to Cm, the tonic. Play Dm7b5, G7, Cm slowly and listen for the way the diminished 5th, Ab, falls to G, the root of the dominant chord, while the minor 7th, C, is already the root of the chord you are heading home to. The Dm7b5 guitar chord shows the shape, and the chord progression builder can build the whole ii–V–i for you.
How to practise half-diminished chords
Practise half-diminished chords inside the ii–V–i progression, because that is where they live. Isolated shapes will not teach you their function.
- Play Bm7b5, E7, Am in A minor, holding each chord for a bar and listening for the pull from ii to V to i.
- On guitar, learn the Bm7b5 guitar chord shape and move it up the neck to find Dm7b5 and Em7b5.
- On piano, play a half-diminished chord with your right hand and the root with your left, then resolve both hands to the dominant 7th a 4th above.
- Play the ii–V–I progression in C major with Dm7, G7 and Cmaj7, then compare it with the minor-key version Dm7b5, G7 and Cm.
- Use the chord finder to build the half-diminished chord on every degree of the minor scale you are practising.
Common mistakes
- Confusing m7b5 with dim7 — A half-diminished chord has a minor 7th, ten semitones above the root, while a fully diminished 7th chord has a diminished 7th, nine semitones above the root. Bm7b5 is B, D, F and A; Bdim7 is B, D, F and Ab. One semitone changes the chord completely.
- Using a half-diminished chord as a tonic — A half-diminished chord is unstable and cannot be a home chord. If your progression keeps landing on one, you have probably mistaken the ii chord for the i chord.
- Leaving out the diminished 5th — The diminished 5th is the note that makes the chord half-diminished rather than minor. Leave out the root or the 7th if you must, but never leave out the 5th, or the chord becomes an ordinary minor 7th.
Quick reference
For example, the half-diminished chord chord on C is C – D# – F# – A#, and every other row follows the same pattern. The table below works out the half-diminished chord chord on six roots so you do not have to. Read down the notes column and notice how the root, minor 3rd, diminished 5th and minor 7th spacing never changes, even though the letter names do, and use the first row as the worked example you can check your own calculations against.
| Root | Half-Diminished Chord notes |
|---|---|
| C | C – D# – F# – A# |
| G | G – A# – C# – F |
| D | D – F – G# – C |
| A | A – C – D# – G |
| E | E – G – A# – D |
| F | F – G# – B – D# |
Once the six rows feel familiar, transpose the table yourself: pick a root that is not listed, work out the notes of the half-diminished chord chord from the interval pattern, and play the result. That single exercise, repeated for a few roots, is what turns a table you have read into a skill you own.
Frequently asked questions
What notes are in a half-diminished chord?
The root, the minor 3rd, the diminished 5th and the minor 7th. Am7b5 is A, C, Eb and G, spelled A, C, D# and G. The 3rd is three semitones above the root, the 5th is six, and the 7th is ten.
Why is it called half-diminished?
Because only the triad is diminished. A fully diminished 7th chord has a diminished 7th as well, nine semitones above the root, while a half-diminished chord has a minor 7th, ten semitones above the root. Half of the chord is diminished, half is not.
Where do half-diminished chords appear?
As the ii chord of a natural minor key. In A minor the ii chord is Bm7b5, in E minor it is F#m7b5, and in D minor it is Em7b5. They also appear in jazz as the ii chord of a minor ii–V–i progression.
What is the difference between m7b5 and dim7?
The 7th. A half-diminished chord (m7b5) has a minor 7th, ten semitones above the root, while a diminished 7th chord (dim7) has a diminished 7th, nine semitones above the root. The triads are identical; only the top note differs.
Can I substitute a minor 7th chord for a half-diminished chord?
No, not safely. A minor 7th chord has a perfect 5th, seven semitones above the root, while a half-diminished chord has a diminished 5th, six semitones above the root. Substituting one for the other removes the tritone that makes the ii–V–i progression work.