Two-Tempo Beat Drift Calculator
How far apart will two fixed-tempo tracks drift after a chosen number of bars?
Method, formula and assumptions
A elapsed seconds = bars x beats per bar x 60 / BPM_A. B's beat advance is elapsed minutes x (BPM_B - BPM_A). The same-beat time difference uses each tempo's duration for the same beat count.
Input definitions and supported units
- Track A tempo (BPM): Measured or assumed numerical value, from 1 to 1000; must be positive.
- Track B tempo (BPM): Measured or assumed numerical value, from 1 to 1000; must be positive.
- Bars counted on A: Whole-number count, from 1 to 100000; must be positive.
- Quarter-note beats per bar: Whole-number count, from 1 to 32; must be positive.
Worked example with answer
32 four-beat bars at 120 BPM last 64 seconds. A 121 BPM track advances 1.0667 beats, reaches beat 128 about 0.5289 seconds earlier, and needs -0.8264% speed correction.
How to use the results
Positive beat advance means B runs ahead; a negative arrival difference means it reaches the corresponding beat earlier. Start-phase errors are separate.
Results retain full precision internally and display up to four decimal places. Very small nonzero results use scientific notation rather than appearing as zero. Check the labels before comparing values across units.
Limitations and references
Assumes steady quarter-note tempos and matching bar structure. Human timing, swing, warped audio and tempo changes require actual alignment measurements.
The method is a self-contained arithmetic, geometric or explicitly stated mathematical model. There are no imported tariffs, empirical presets or equipment specifications; measured values and allowances must come from your own process.
Related planning tools
Creator & reviewers
Creator persona
- Casey RowanUnits, conversions & measurement
Reviewer personas
- Devon ShawFormula & assumptions review
- Sage MitchellClarity & usability review