Some musical concepts feel intimidating at first. Altered chords were one of them for me. They sound dense, the notation looks complex, and most explanations dive straight into theory without ever explaining what an altered chord actually is. But once you understand them, there's a big chance you'll fall in love with the sound. They're the engine behind some of the most expressive moments in jazz and modern harmony.

This guide breaks down what an altered chord is, the altered scale it comes from, how to build one in any key, and when to use altered chords in your own writing.

What is an altered chord?

An altered chord is a dominant seventh chord (a V7) where the tensions — the 9th, 11th, and 13th — have been altered, meaning raised or lowered by a half-step. The result is a chord with maximum tension that wants to resolve, hard, to the tonic chord.

The most common written form is C7alt, G7alt, D7alt, and so on. The "alt" symbol tells the performer to alter every available tension: ♭9, ♯9, ♯11, and ♭13. You don't usually play all of those at once — the symbol gives the improviser permission to use any combination of them.

The altered scale (super locrian)

Altered chords come from the altered scale, also called the super locrian, the diminished whole-tone scale, or the Ravel scale. The intervals are:

Root - ♭9 - ♯9 - 3 - ♯11 - ♭13 - ♭7

In C, that's: C - D♭ - D♯ - E - F♯ - A♭ - B♭

You can think of it as the seventh mode of the melodic minor scale. If you play a D♭ melodic minor scale starting on C, you get the C altered scale. That's the easiest way to find it on your instrument: pick a melodic minor scale a half-step above your root, and start it from the chord's root.

How to build an altered chord

To build a C7alt, take the C7 chord (C - E - G - B♭) and stack altered tensions on top. The full chord tones and altered extensions are:

Root - 3 - ♭7 - ♭9 - ♯9 - ♯11 - ♭13

For C7alt: C - E - B♭ - D♭ - D♯ - F♯ - A♭

In practice, you almost never voice all seven notes. A typical altered voicing keeps the 3rd and ♭7th (the chord's identity) and adds two or three altered tensions on top. A common piano voicing for C7alt is just E - B♭ - D♭ - A♭ — root in the bass, 3rd, ♭7th, ♭9, and ♭13. That four-note voicing already captures the altered sound completely.

Why these tensions?

The altered chord works because each altered tension creates a half-step pull toward the chord of resolution. If C7alt resolves to F, then:

  • The ♭9 (D♭) pulls down to C (the 5th of F)
  • The ♯9 (D♯) pulls up to E (the 7th of F)
  • The ♯11 (F♯) pulls down to F (the root)
  • The ♭13 (A♭) pulls down to G (the 9th of F)

Every altered note is in tension with the target chord and resolves by half-step. That's what gives the altered sound its inevitable "needs to resolve" quality.

When to use altered chords

Altered chords work best as dominant chords resolving to a tonic — anywhere you'd normally play a plain V7, you can try V7alt for more color and pull. Here are three favorite resolutions:

IIm7♭5 - V7alt - Im7 — the classic minor ii-V-i. The altered V7 over a minor cadence is one of the most authentic-sounding moves in jazz.

IIm7 - ♭II7alt - Imaj7 — a tritone substitution. Instead of resolving V7 down a fifth, you substitute it with ♭II7alt and resolve down by half-step. This is the sound behind countless Brazilian and modern jazz progressions.

V7alt to a major chord — even in major keys, altering the V7 adds bite. Try replacing G7 with G7alt before resolving to Cmaj7.

Where you'll hear altered chords

Bebop and post-bop standards use altered dominants constantly. Listen to recordings of "Stella by Starlight," "All the Things You Are," or "Giant Steps" and you'll hear V7alt voicings on almost every dominant. Brazilian composers like Tom Jobim and modern players like Brad Mehldau use them in lush ballad arrangements. Even pop music borrows them — listen to the dominant chords in Stevie Wonder's "You Are the Sunshine of My Life" or in Steely Dan's catalog.

How to practice altered chords

The fastest way to internalize altered chords is to play them in context. Open Flat, write a simple ii-V-I in C major, then replace the G7 with G7alt and listen to the difference. Try the same in a few different keys until the altered sound becomes familiar to your ear. Once you hear it as "the chord that wants to resolve," you'll start spotting it everywhere.

Don't be afraid to experiment.