Transpose Calculator - Shift Keys & Chords by Semitones

Transposition moves every note of a piece by the same interval, keeping all the relationships between notes intact — a song in C major shifted up two semitones becomes the identical song in D major. Musicians reach for it constantly: singers move a song into a comfortable range, guitarists avoid awkward barre shapes or plan where to put a capo, and horn players convert between written and concert pitch. This calculator does the mechanical part: paste a progression like C, Am, F, G, set the shift, and read the new progression instantly. The math works on pitch classes. Each of the twelve notes in an octave gets a number from 0 (C) to 11 (B); sharps and flats that name the same key on a piano share a number, so C# and Db are both 1. To transpose, the calculator adds the semitone shift to each root's number, wraps around at 12, and converts back to a name. The chord quality — everything after the root, like m, 7, maj7, dim, or sus4 — never changes under transposition, so the calculator copies it verbatim: Am up 2 becomes Bm, and F#m7b5 up 1 becomes Gm7b5. Because each pitch class has two possible names, the calculator needs a spelling rule, and it uses a deliberately simple one: if any root you typed is spelled with a flat and none with a sharp, the answer is spelled with flats (Db, Eb, Gb, Ab, Bb); in every other case it prefers sharps (C#, D#, F#, G#, A#). That matches the common convention that flat keys stay flat and sharp keys stay sharp, though a fully key-aware engraver might occasionally choose the other enharmonic spelling — the sounding pitch is identical either way. The presets cover the most common transposing instruments. A Bb instrument such as trumpet, clarinet, or tenor sax sounds a whole step lower than written, so to write a part that sounds at concert pitch you transpose the concert notes up 2 semitones. Eb instruments (alto and baritone sax) read parts written up 9 semitones (a major sixth), and F instruments (French horn, English horn) read parts written up 7 semitones (a perfect fifth). In each case the printed part sits higher than the sounding pitch, and the written parts may also land an octave up or down depending on the instrument's range — the note names this calculator gives are what matters for reading and fingering. Going the other way — working out what a transposing instrument actually sounds — just flips the sign: a written D on a Bb trumpet sounds as concert C, i.e. down 2 semitones. Negative numbers in the semitone field handle that directly.