A Half Diminished
Hear the A Half Diminished chord played for you.
Aø7
A – C – D♯ – G
Formula:R-m3-d5-m7
Intervals:P1-m3-d5-m7
Scale Degrees:1-b3-b5-b7
Introduction
The A Half Diminished chord is a four-note chord made up of A, C, D♯, and G. It is built from a root, minor third, diminished fifth, and minor seventh.
The A Half Diminished piano chord (Am7b5) consists of the notes A, C, D#, G. It is a diminished triad with an added minor 7th, giving it a dark, moody, and tense character commonly used in jazz and minor key progressions. Formula: R-m3-d5-m7 | Scale degrees: 1-b3-b5-b7.
Notes
A Half Diminished Inversions
| Position | Notes |
|---|---|
| Root Position | A – C – D# – G |
| 1st Inversion | C – D# – G – A |
| 2nd Inversion | D# – G – A – C |
| 3rd Inversion | A – C – D# – G |
Key Signature
The key of A Half Diminished has 3 sharps.
F♯C♯G♯
Order of sharps
Sharps are added to a key signature in a fixed order. Each new sharp key adds the next sharp on the list.
F♯C♯G♯D♯A♯E♯B♯
Mnemonic: Father Charles Goes Down And Ends Battle
Chords in the Key of A Major
These are the diatonic triads built on each degree of the A major scale:
C
D
E
F
G
A
B
C
D
E
F
G
A
B
I — A Major (major)
Theory: Intervals
Formula: R-m3-d5-m7
Intervals: P1-m3-d5-m7
The A Half Diminished is built by stacking intervals from the root note. The formula R-m3-d5-m7 describes the scale degrees used. The intervals P1-m3-d5-m7 show the distance between each note in the chord.
A Half Diminished — Frequently Asked Questions
What notes are in the A Half Diminished chord?
Am7b5 contains: A, C, Eb, G. Diminished triad with minor seventh.
How does Am7b5 differ from Adim7?
Minor seventh (G) vs diminished seventh (Gb).
How is Am7b5 used?
ii chord in G minor (Am7b5–D7–Gm). Very common in jazz.
What songs use Half Diminished?
Autumn Leaves uses Am7b5 in G minor. One of the most common half-diminished chords.
How does Am7b5 differ from Am7?
Flatted fifth (Eb vs E).
Is Am7b5 the same as Cm6?
Same four notes (A, C, Eb, G = C, Eb, G, A). Context determines the name.
Practice Tips
- Minor-key ii–V–i in G minor: Am7b5 → D7 → Gm — this is in Autumn Leaves.
- Am7b5 and Cm6 are the same notes.
- One of the most common half-diminished chords in jazz.
- Compare with Adim7 and Am7.
- The Eb creates the half-diminished tension.
- Nearly all white keys plus Eb.
Related Tools
Chord FinderLook up any chord — see the notes, hear it, and play along.Chord DrillTimed drills to build speed and recognition across all chord types.Practice RoomPlug in a MIDI keyboard and get real-time feedback on every chord and scale.Circle of FifthsVisualize key relationships, relative minors, and key signatures.MIDI MonitorLive MIDI message stream with note names, velocity, and a scrolling staff.