Chord Extensions & Tensions
Updated: 2026-07-06A seventh chord is the baseline; the color comes from what you stack on top. Keep piling thirds above the seventh and you reach the 9th, 11th, and 13th — the extensions — plus their sharpened and flattened cousins, the alterations. These are what give jazz chords their lush, spicy sound.
Key takeaways
- Keep stacking thirds above the 7th to get the 9th, 11th, and 13th (extensions).
- On dominant chords you can alter tensions: ♭9, ♯9, ♯11, ♭13.
- Extensions add color; alterations add tension that wants to resolve.
- Some tensions are "available," some are "avoid" — the natural 11 clashes over major and dominant chords.
This lesson builds on Seventh Chords in Jazz.
What are the 9th, 11th, and 13th?
They're the next notes in the third-stack above the seventh — the 2nd, 4th, and 6th of the scale, moved up an octave. On C, the 9th is D, the 11th is F, the 13th is A. C9 = C–E–G–B♭–D, and C13 = C–E–G–B♭–D–A.
In practice you rarely play all of them at once; you pick the color you want (a 9 here, a 13 there) and often drop the root and 5th.
What are altered tensions?
On dominant chords you can raise or lower the 9th and 13th to create extra tension: ♭9, ♯9, ♯11, ♭13. These "wrong" notes sound unstable — which is exactly the point, because a dominant chord wants to resolve. C7♭9 = C–E–G–B♭–D♭.
Listen
- Extended chord on Wikipedia — hear 9/11/13 colors.
- Altered chord on Wikipedia — the sound of altered dominants.
Practice
Take a ii–V–I in C. Add a 9 to the Dm7, keep the G7 plain, then add a 13 to the G7 and a 9 to the Cmaj7. Then try a ♭9 on the G7 and hear the extra tension resolve into C. Do it in all 12 keys.
Common mistakes
- Voicing extensions low in the bass — 9/11/13 turn to mud down there; keep them high.
- Stacking every alteration at once — pick two or three tensions, not all of them.
- Using the natural 11 over a major or dominant chord — it clashes with the 3rd; use ♯11 instead, or the 11 only on minor chords.
Frequently asked questions
What's the difference between an extension and a tension? They're the same notes (9, 11, 13) — "extension" describes the note as an added color, while "tension" emphasizes that it creates instability wanting resolution, especially when altered on a dominant chord. In casual jazz talk the words are used interchangeably.
Which alterations go on which chord? Alterations (♭9, ♯9, ♯11, ♭13) live almost exclusively on dominant chords resolving to a tonic. On major and minor chords you use natural extensions (9, 13, and 11 only on minors); ♯11 is the exception you'll add to major chords for a Lydian color.
Now that you can color the chords, let's learn to read them off the page — continue with Reading Lead Sheets.