Root, third and seventh: the guide tones fix the quality, so the fifth is dropped. That is what leaves a string free, so pick a tension to put on top.
Bbmaj7#5 is Bb, D, F# and A — Bbmaj7 with the fifth raised a semitone.
It sounds weightless, with no pull in it. Unlike an aug7 there is no flat seventh dragging it anywhere, so it colours a tonic rather than replacing it with a dominant.

| Bb | D | F# | A |
|---|---|---|---|
| 1 | 3 | ♯5 | 7 |
Tonic — the lydian augmented sound.
Also written BbM7#5, BbΔ7#5, Bb+M7 or Bbmaj7(#5). The same chord either way; which spelling you meet depends on who wrote the chart.
Root, third and seventh. The third and seventh, the guide tones, are what make the chord major, minor or dominant, so the fifth can go: it says nothing the symbol needs.
Three notes means a spare string, which is the real point. Put a tension on it.
Bbmaj7#5 has 4 of them, on strings 5-3-2-1 and strings 6-4-3-2, from open position up to the 13th — all in one inversion, so the bass note never moves. The one to learn first is the Bb shape at the nut.
Start with x10232 — no barre and 1 open string. 1 of the 8 shapes here sits in open position. 1 of the 8 needs a barre. Together they cover the neck from the 1st fret to the 14th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| x10232 | open position | Bb, root position | F# | 1 open string |
| x1423x | 1st fret | Bb, root position | D | all fretted |
| xx4335 | 3rd fret | F#, 2nd inversion | A | all fretted |
| xx8775 | 5th fret | Bb, root position | A | all fretted |
| 6x7776 | 6th fret | Bb, root position | Bb | barred |
| x-x-8-11-10-10 | 8th fret | Bb, root position | D | all fretted |
| x-13-12-11-10-10 | 10th fret | Bb, root position | D | all fretted |
| x-13-12-14-x-14 | 12th fret | Bb, root position | F# | all fretted |
The same notes rebuilt from scratch give 13 drop 2, 9 drop 3 and 6 open string voicings, each on its own page.
Tensions. A shell of Bbmaj7#5, root, third and seventh, leaves a string free, and the tones that belong over it are the 9 (C), the #11 (E) and the 13 (G).
How you get to it. The turn that lands on Bbmaj7#5 is Cm7 to F7 — the ii and the V of Bb — and F7 shares its third and seventh with Cm7, so the hand barely moves between them.
Change one note of Bbmaj7#5 and you have Bbmaj7 (the sharp fifth becomes a fifth), Bbmaj7b5 (the sharp fifth becomes a flat fifth), Bbaug (drop the major seventh) or Bbaug7 (the major seventh becomes a flat seventh).
Bbmaj7#5 is a major chord — root, major third, fifth. Major chords on every root.
On Bbmaj7#5’s sound and use this page follows Mark Levine, The Jazz Theory Book (Sher Music, 1995). The shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.