C#m7b5 Chord on Piano
C#m7b5 = C# – E – G – B (Root, Minor 3rd, Tritone, Minor 7th)
C# sits on the first black key in the two-black-key group, wedged between C and D (some scores spell it Db instead of C#, same key, different name), and building a half-diminished 7th chord on top of it gives you C#, E, G, B. The result is unsettled — the flatted 5th removes any sense of stability — it functions as the half-diminished viiø7 in D major, or the iiø7 chord that opens a minor-key ii–V–i. On piano, C#m7b5 block-style and the shape is four notes that typically land under fingers 1, 2, 3, and 5, or 1, 2, 4, 5 if that fits better; 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. That's 4 notes total, counting the root — worth knowing before you look at a written voicing and wonder if a note's missing.
Functionally, this voicing serves as the half-diminished viiø7 in D major, or the iiø7 chord that opens a minor-key ii–V–i — that's where you'll meet it most, in written scores and in improvised comping alike. The whole shape fits comfortably under one hand for most adult spans, which makes it a natural chord to drill hands-separately before combining it with a moving bass line. Slide E down to the bass and the rest of the notes stack above it for first inversion — with four notes involved, which inversion you use often matters more than sticking rigidly to root position. Genre-wise it's common in film-noir underscoring and shows up again in bossa nova minor progressions. C#'s position on the keyboard (the first black key in the two-black-key group, wedged between C and D) means the thumb or index finger typically has to reach up onto the black key while the rest of the hand stays anchored on the surrounding white keys. In a band context the left hand typically thins the chord down to the root and maybe the 7th, leaving the right hand to carry the rest of the color — playing every note of the full stack in both hands just muddies the low end. Played around middle C it reads as a comping chord; move the same shape down two octaves and it reads as a bass-register power move instead, and up two octaves it turns airy and bell-like — the notes don't change, only where they sit on the keyboard. Trained ears learn to spot C#m7b5 by that unsettled — the flatted 5th removes any sense of stability quality before naming a single note — the color usually gives it away faster than working out the interval structure by ear.
Voicings
Root Position
First Inversion
How to Practice It
Start with C#m7b5 in root position, right hand only, using fingers 1-2-3-5, or 1-2-4-5 if that sits more naturally under your hand. Play it slowly enough to check that every key is actually depressed together — black-key chords are easy to half-press if the hand angle is off. Once the root-position shape is solid, work the inversion(s) the same way, then add the left hand playing just the root (or root and fifth) an octave below. A metronome at a slow tempo will expose any notes that land a fraction of a second apart before you speed up. Finally, practice moving into and out of C#m7b5 from a neighboring chord in the same key so the hand-shape change becomes automatic rather than something you have to think through each time. 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: C#m7b5 opening a minor ii–V–i in B minor
- viiø7 – I: C#m7b5 resolving up a half step into D major
- C#m7b5 as a dark pre-dominant chord just before the V7 in a minor key
FAQ
- What notes make up C#m7b5 on piano?
- C#m7b5 is built from C#, E, G, B — C# as the root, with the rest of the half-diminished 7th formula stacked above it. Play them left to right in that order for root position; inversions just reorder which note sits lowest.
- Do I need to play all 4 notes of C#m7b5 in one hand?
- Most players can, since it stays within a single hand span, but splitting the root into the left hand while the right hand plays the remaining notes is a completely normal alternative, especially in a fast progression.
- How does C#m7b5 usually function in a progression?
- It typically works as the half-diminished viiø7 in D 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 C#m7b5?
- Raise the flatted 5th back up a half step and C#m7b5 becomes a plain minor 7th chord — the lowered 5th is what pushes it from merely mellow into genuinely unstable.
C#m7b5 on other instruments: C#m7b5 on Guitar. Related: how chords are built, chord finder.