About

Transposing chords by hand introduces errors. A single wrong enharmonic spelling - writing G# when the key demands Ab - makes a chart unreadable to other musicians and breaks sight-reading flow. This tool maps every chord root to its chromatic index (0 - 11), applies the semitone offset modulo 12, and resolves the correct enharmonic spelling based on the target key signature. It preserves chord quality suffixes (m7, sus4, dim, slash bass notes) and maintains original text formatting so lyrics stay aligned.

Limitation: the parser assumes standard Western 12-TET tuning. Microtonal systems and non-Latin note names (Do-Re-Mi solfège) are not supported. Chord detection uses pattern matching; unusual spacing or non-standard notation (e.g., H for B in German convention) may require manual correction.

Formulas

Each note in the chromatic scale is assigned an integer index i from 0 (C) to 11 (B). To transpose a chord root by s semitones:

i_new = (i_original + s) mod 12

The modulo operation ensures the result wraps within the 12-tone cycle. Enharmonic resolution follows standard key-signature convention: keys with sharps in their signature (G, D, A, E, B, F#) produce sharp spellings; keys with flats (F, Bb, Eb, Ab, Db, Gb) produce flat spellings.

For slash chords, the bass note after the / is transposed independently using the same formula. The chord quality suffix (e.g., m7, sus4, add9) passes through unchanged.

Where i_original = chromatic index of the source note, s = signed integer semitone shift (−11 to +11), i_new = chromatic index of the transposed note.

Reference Data

Semitones	Interval Name	From C	From G	From D	From A	From E	From F
0	Unison	C	G	D	A	E	F
1	Minor 2nd	Db	Ab	Eb	Bb	F	Gb
2	Major 2nd	D	A	E	B	F#	G
3	Minor 3rd	Eb	Bb	F	C	G	Ab
4	Major 3rd	E	B	F#	C#	G#	A
5	Perfect 4th	F	C	G	D	A	Bb
6	Tritone	F#/Gb	C#/Db	G#/Ab	D#/Eb	A#/Bb	B/Cb
7	Perfect 5th	G	D	A	E	B	C
8	Minor 6th	Ab	Eb	Bb	F	C	Db
9	Major 6th	A	E	B	F#	C#	D
10	Minor 7th	Bb	F	C	G	D	Eb
11	Major 7th	B	F#	C#	G#	D#	E
12	Octave	C	G	D	A	E	F

Frequently Asked Questions

The tool uses the Circle of Fifths convention. If the target key signature contains sharps (G, D, A, E, B, F#), enharmonic notes are spelled with sharps (e.g., C# instead of Db). If the target key contains flats (F, Bb, Eb, Ab, Db, Gb), flat spellings are used. When no key is specified, the tool defaults to the sharp/flat preference of the original input chords.

Yes. The parser isolates the bass note after the forward slash and transposes it independently using the same semitone offset and enharmonic rules as the root. For example, C/E transposed up 2 semitones becomes D/F#.

The parser preserves any suffix following the root note and optional accidental. This includes m, maj, min, dim, aug, sus2, sus4, add9, add11, 6, 7, 9, 11, 13, M7, m7b5, dim7, and compound suffixes like m7add11. The suffix is treated as an opaque string and is not modified during transposition.

Because 12-TET is a cyclic system with 12 semitones per octave. Transposing up by s semitones is equivalent to transposing down by 12 − s semitones. So +5 and −7 both shift by the same interval (a perfect fourth up or a perfect fifth down).

Yes. The tool identifies chords using pattern matching (capital letter A - G followed by optional accidentals and quality suffixes). Non-chord text, lyrics, whitespace, and line breaks are preserved exactly. Column alignment of chord-over-lyric sheets is maintained.

Both. If you specify a source key, the tool calculates the destination key and displays it. Every chord root (and slash bass note) in the text is individually transposed by the same interval. The relationship between chords is preserved, ensuring harmonic function stays identical.