Chord · B Diminished 7th
Bdim7 Chord
Bdim7 is B, D, F and Ab — symmetrical; passes through every key. Used as a dominant substitute.
Bdim7 on every instrument
The same 4 notes, 6 sets of hands. Open a diagram for alternate shapes, audio and the mistakes to avoid.
What Bdim7 is made of
B Diminished 7th (B diminished 7th) is built from the notes B, D, F, Ab, with the interval pattern 1, b3, b5, bb7. A common diminished 7th chord across many styles.
Stack 1, b3, b5 and bb7 on a root of B and you get B, D, F and Ab. That interval recipe is what makes the chord a diminished seventh chord — move the same shape to another root and the character travels with it, which is why Cdim7 sounds like a transposed Bdim7.
Diminished 7th: Symmetrical; passes through every key. Used as a dominant substitute.
Spelling: the notes above are written the way a score would write them, not simplified to the nearest piano key. That is why this chord is spelled with A♭ rather than its enharmonic equivalent.
Keys that contain Bdim7
No major or natural-minor key contains all 4 of these notes — this one gets borrowed.
Chords like this one sit outside the diatonic set — they arrive as secondary dominants, borrowed chords or passing harmony. Browse every key to see which progressions pull it in.
Other chords on B
Same root, different colour.
The same diminished seventh shape, moved
The identical interval recipe, built on other roots.
Questions people ask about Bdim7
- What notes are in the Bdim7 chord?
- Bdim7 is made of B, D, F and Ab — the 1, b3, b5 and bb7 degrees of a diminished seventh chord built on B.
- What keys use the Bdim7 chord?
- No major or natural-minor key contains all 4 notes of Bdim7. Chords like this arrive as borrowed harmony — secondary dominants, harmonic-minor colour, or chromatic passing chords — rather than as one of a key's native chords.
- How do you play Bdim7 on guitar and piano?
- This page shows Bdim7 on guitar, piano, ukulele, bass, mandolin and banjo — 9 voicings in total. Each diagram links to the full instrument page with alternate shapes, audio and common mistakes.
Learn the theory behind it
Why Bdim7 behaves the way it does — the guides that explain the chord instead of just spelling it.