A#m7b5 Chord on Piano
A#m7b5 = A# – C# – E – G# (Root, Minor 3rd, Tritone, Minor 7th)
Stack the half-diminished 7th formula on A# and you land on A#-C#-E-G#, a chord that sounds the tensest 'minor-family' chord in common use. A# itself is the last black key of the three-black-key group, just before B on the keyboard. Grabbed as a single root-position block, A#m7b5 ends up less than a full octave in root position, so most hands cover it without strain. Functionally this is the half-diminished viiø7 in B major, or the iiø7 chord that opens a minor-key ii–V–i, and the flatted 5th removes the stable perfect fifth a minor 7th chord would otherwise have, so it almost always keeps moving toward a dominant chord next. In total that's 4 notes with the root included — good to have in mind before checking a written voicing against it.
Think of A#m7b5 primarily as the half-diminished viiø7 in B major, or the iiø7 chord that opens a minor-key ii–V–i — that's what it's doing most of the time, in a lead sheet or in the moment. Put C# on the bottom instead of A# and you've got first inversion; four-note chords like this one get used in inversion at least as often as they get used in root position. Since the reach stays well within a normal hand span, there's no excuse to skip clean hands-separate practice before adding a moving bass line under it. It shows up regularly in bossa nova minor progressions, and again in classical half-diminished passing chords. The flatted 5th removes the stable perfect fifth a minor 7th chord would otherwise have, so it almost always keeps moving toward a dominant chord next. Since last black key of the three-black-key group, just before B, a black-key root asks the hand to angle slightly forward, a small adjustment that stops feeling foreign after enough repetition. With bass covered elsewhere, the left hand's job shrinks to root (sometimes root and 7th), freeing the right hand to focus on the color tones that make this voicing worth using in the first place. Register changes the personality here more than almost anything else — this shape near middle C is a normal comping voicing, shifted low it reads as a bass gesture, and shifted high it turns delicate and glassy. The fastest way to internalize A#m7b5 is by sound, not by spelling — that the tensest 'minor-family' chord in common use quality becomes instantly recognizable long before the notes are memorized by name.
Voicings
Root Position
First Inversion
How to Practice It
Drill the right hand alone first, fingers whichever of 1-2-3-5 or 1-2-4-5 keeps your wrist level; both are standard choices for this shape landing on A#, C#, E, G# together as one block. A# being a black key means the hand needs a slight forward tilt to press it evenly with its white-key neighbors — check that in a mirror or on video if it feels off. Add the left hand's root note only once the right hand is solid, then work both hands together at a tempo slow enough that nothing rushes. Finish by walking into A#m7b5 from whatever chord comes before it in context, repeating that specific transition until it's automatic. It's easy to confuse this with a plain minor 7th at a glance; the flatted 5th is the one note that makes the whole chord function differently, so isolate and check it specifically.
Common Progressions
- iiø7 – V7 – i: A#m7b5 opening a minor ii–V–i in G# minor
- viiø7 – I: A#m7b5 resolving up a half step into B major
- A#m7b5 as a dark pre-dominant chord just before the V7 in a minor key
FAQ
- What notes make up A#m7b5 on piano?
- A#, C#, E, G# — that's A#m7b5, A# plus the rest of the half-diminished 7th shape built on top. Root position keeps them in that left-to-right order on the keyboard; any inversion just moves a different one of those notes to the bottom.
- Can A#m7b5's 4 notes be split between the hands instead of played together?
- In most cases, yes, one hand covers it comfortably — but splitting the root off to the left hand is common practice too, not a sign you're doing it wrong.
- What Roman-numeral role does A#m7b5 usually play?
- In practice, as the half-diminished viiø7 in B major, or the iiø7 chord that opens a minor-key ii–V–i. The flatted 5th removes the stable perfect fifth a minor 7th chord would otherwise have, so it almost always keeps moving toward a dominant chord next.
- What's the closest related chord to A#m7b5?
- Raise the flatted 5th back up a half step and A#m7b5 becomes a plain minor 7th chord — the lowered 5th is what pushes it from merely mellow into genuinely unstable.
A#m7b5 on other instruments: A#m7b5 on Guitar. Related: how chords are built, chord finder.