Estimate time to finish an audiobook.
An audiobook's stated runtime assumes 1x playback, so listening faster divides the real time you spend. Dividing runtime by playback speed gives the hours you will actually sit through, and dividing that by your daily listening habit gives the calendar days to the last chapter. The hours saved figure shows what the speed bump actually buys, which is often the difference between finishing a book in a fortnight and abandoning it.
Effective listening time
Listening hours = stated runtime / playback speed
Days to finish
Days = listening hours x 60 / listening minutes per day
Most listeners adapt to 1.25x to 1.5x within a chapter with little loss. Beyond about 2x comprehension of dense non-fiction drops noticeably, though familiar or narrative material holds up better.
Because missed days are not modelled. Enter your realistic weekly average divided by seven rather than an ideal daily session.