Compare buying new, used, e-book and library options.
Reading cost depends far more on where books come from than on how many you read. Library borrowing removes the price entirely, used copies typically cost a third of new, and the blended average per book read is the figure worth tracking. Comparing your blend against an all-new baseline shows exactly what sourcing habits are worth over a year.
Blended reading cost
Yearly spend = books read x (1 - library share/100) x used price; average per book = yearly spend / books read
Raise the library share first — it removes cost rather than reducing it — then buy used for titles you want to keep. Both levers show up immediately in the average cost per book read.
Enter their price in the used-price field if that is your normal purchase route; the arithmetic is the same, only the unit price changes.
It is comparable across years even when your reading volume changes, which makes it a better habit metric than total spend.