What notes are in a B♭ half-diminished chord?

B♭ half-diminished contains four notes: B♭ (root), D♭ (minor third), F♭ (diminished fifth — same pitch as E), and A♭ (minor seventh).

Is B♭m7♭5 the same as A♯m7♭5?

Enharmonically yes — same four pitches. B♭m7♭5 is the flat-side spelling; A♯m7♭5 is the sharp-side. In practice both are rare; G♯m7♭5 covers the most common harmonic territory for this pitch set.

Why is the fifth F♭ instead of E?

The half-diminished chord builds on a diminished triad (root, ♭3, ♭5). From B♭, the fifth letter is F; the diminished version of F natural is F♭. Calling the note E would skip the F letter entirely.

When would I see B♭m7♭5 in real music?

Rarely as a tonic-key iiø7 — A♭ minor is essentially never used. The chord appears in late-Romantic chromatic harmony as a colour or in jazz as a substitute for E7♭9 (tritone-related dominant).

Bb half-diminished chord — notes, intervals, and practice

B♭ half-diminished (B♭m7♭5 or B♭ø) — B♭, D♭, F♭, A♭ — is the iiø7 of A♭ minor (theoretical) and a deeply flat-side chord. The F♭ (enharmonic to E natural) is the spelling tell. In practice the chord is more often written as A♯m7♭5 in sharp-key contexts, but flat-side music inside A♭ minor uses this spelling.

Intervals

The Bb half-diminished chord stacks two thirds on the root. Each interval and its size in semitones:

Bb→Dbminor 3rd3 semitones
Db→Fbminor 3rd3 semitones
Fb→Abmajor 3rd4 semitones

On the keyboard

Each note of the Bb half-diminished chord highlighted on a piano. Pitch class is what matters — any octave works.

On the guitar

One voicing of the Bb half-diminished chord on a six-string guitar fretboard.

Common mistakes

B♭m7♭5's fifth is F♭, enharmonic to E. Inside A♭-minor key context (which itself is rare) the F♭ spelling preserves consistency. In jazz lead-sheet practice the chord is sometimes written B♭m7♭5 with E as the fifth — strictly incorrect but common. The all-flat spelling is unusual visually because most flat-key chords use only one or two flats.

In context

B♭m7♭5 → E♭7 → A♭m is the theoretical ii–V–i in A♭ minor. Since A♭ minor is essentially never used as a tonic, this progression is rare. The chord appears more often as a chromatic colour in late-Romantic harmony or as a tritone-substitute setup in jazz.

Drill it

The Bb half-diminished chord is one of 48 in the Chord Trainer. Open the full trainer to practice it alongside related chords with timing and best-time tracking.

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Frequently asked

What notes are in a B♭ half-diminished chord?: B♭ half-diminished contains four notes: B♭ (root), D♭ (minor third), F♭ (diminished fifth — same pitch as E), and A♭ (minor seventh).
Is B♭m7♭5 the same as A♯m7♭5?: Enharmonically yes — same four pitches. B♭m7♭5 is the flat-side spelling; A♯m7♭5 is the sharp-side. In practice both are rare; G♯m7♭5 covers the most common harmonic territory for this pitch set.
Why is the fifth F♭ instead of E?: The half-diminished chord builds on a diminished triad (root, ♭3, ♭5). From B♭, the fifth letter is F; the diminished version of F natural is F♭. Calling the note E would skip the F letter entirely.
When would I see B♭m7♭5 in real music?: Rarely as a tonic-key iiø7 — A♭ minor is essentially never used. The chord appears in late-Romantic chromatic harmony as a colour or in jazz as a substitute for E7♭9 (tritone-related dominant).