B♭ Major
0 - 4 - 7Root + major 3rd + perfect 5th
About B♭ Major
B♭ major is the barre chord that guitarists learn last and horn players learn first. Its notes — B♭, D, F — sit at the heart of brass music, and none of them is an open string on this instrument. The shape is an A major moved up one fret, with the index finger holding everything below it.
The notes
B♭, D, F — root, major third, perfect fifth. The D and F are common enough on guitar; the B♭ is the outsider, a semitone below the open B string and a semitone above the A.
That proximity is what makes the chord awkward: the hand is working between two open strings it cannot use, in the first two frets where the action is highest.
Two shapes and a shortcut
The A-shape barre at the first fret is standard and hard. The E-shape barre at the sixth fret is the same chord, easier to hold, and higher in pitch — the usual choice when the bass is covered by another instrument.
The shortcut is a capo at the third fret and a G shape, or at the first with an A shape. Both produce B♭ with none of the effort, and both are used on countless recordings.
Where it shows up
As the tonic of its own key, the IV of F major and the V of E♭. Jazz standards, big band charts and school wind music all cluster here for the same reason: transposing instruments read C and sound B♭.
For a guitarist the most common encounter is as the ♭VII in the key of C — a borrowed chord that appears constantly in rock, where B♭ before F or C sounds like a lift rather than a modulation.