Tool

Progression analyser

A sequence of chord symbols read in a key: degree, function, and what each chord is doing there.

Write the chord symbols separated by spaces and choose the key. Each chord is read as a degree of that key, with its function, and the reading says what it is doing there — diatonic, borrowed, a secondary dominant, a tritone substitution.

Chord symbolsKey

Symbol	Degree	Function	Reading
Cmaj7	Imaj7	Tonic	Degree Imaj7 of the harmonic field of C major.
A7	V7/ii	Dominant	Secondary dominant: it prepares degree ii7.
Dm7	ii7	Subdominant	Degree ii7 of the harmonic field of C major.
G7	V7	Dominant	Degree V7 of the harmonic field of C major.
Em7	iii7	Tonic	Degree iii7 of the harmonic field of C major.
Fm	iv	Subdominant	Borrowed from the parallel minor mode: it is the iv of C minor.
Cmaj7	Imaj7	Tonic	Degree Imaj7 of the harmonic field of C major.

Candidate keys

How many chords in the sequence belong to each key's harmonic field. It is a ranking, not an answer: the tool does not separate relatives, and a sequence that modulates belongs to more than one.

5 of 7
5 of 7
B♯ major 5 of 7
3 of 7
3 of 7

Harmonic analysis

Harmonic analysis reads each chord of a progression as a degree of the key, written as a roman numeral. In C major, Dm7 G7 Cmaj7 is ii–V–I; in F major, the same progression is Gm7 C7 Fmaj7. The chord symbols change from key to key, and the degrees stay the same.

Function

Each degree has a function: tonic, subdominant or dominant. The ii–V–I progression moves from the subdominant to the dominant and ends on the tonic, the most common way to close a phrase in tonal music.

Chords from outside the key

A chord outside the key's harmonic field has a reading too. A secondary dominant is the dominant of another degree: in C major, A7 is V7/ii, the dominant of Dm. A borrowed chord comes from the parallel key: Fm in C major comes from C minor and reads as iv. A tritone substitution replaces a dominant with the one a tritone away: D♭7 in place of G7, before C.

Key

The analysis depends on the key chosen: Am is vi in C major and i in A minor. The candidate keys are listed in order of how many of the progression's chords belong to the harmonic field of each.

Read about

Roman numeral analysisThe notation that describes a chord by the position it occupies in the key rather than by the note it sits on.
Harmonic functionThe role each degree plays — tonic, subdominant, or dominant — and the tension that moves one to the next.
Diatonic harmonyThe chords that arise from stacking thirds on each degree of a scale, and why each quality lands where it does.
Secondary dominantsChords from outside the key that act as the dominant of some degree other than the first.
Modal interchangeChords taken from the parallel key, changing a degree's colour without changing the centre.
Tritone substitutionReplacing a dominant with the one a tritone away, which shares its inner tritone.
CadencesThe formulas that close a phrase, and the degree of finality each one delivers.