It& #39;s well known that the NPV() function in Excel is wrong, in that it assumes that the first cell indexes to 1 rather than 0. Having implored my students for the 200th time to not use it and just code the NPV as an in place sum, I speculated as to why it was like this.
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I guessed out loud that Excel for Windows had just copied the original Excel for Mac which had just copied Lotus 1-2-3 (which had likely just copied what VisiCalc did.) I decided to check...
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Here are the manual entries for Lotus 1-2-3 (v1) and for VisiCalc (v1).

So in 2021, legions of financial analysts are completely screwing up their NPV calculations because of a decision made 40+ years ago by Dan Bricklin in a software program for the Apple II.

¯\_(ツ)_/¯