Excel calculates that A1 should be 11.73% ie a 12% return pa.

I've used a compounding calculator and it comes out the same 11.73% (so, I must think if the excel formula comes out with the same numbers (11.73%)....would it not also be using compounding).

So, if we didn't have any compounding should it not be 64%?

I may be a bit thick here but if I use the 2nd example:

Say, I lent $5,000 to a company at 64% annual interest (simple interest and no compounding). They would owe me $3,200 per year in interest. This $3,200 is not added to principle it just accrues and earns no interest. At the end of 25 years the would owe me $3,200 x 25 = $80,000. Since he was paying me 64% per year would not my return be 64% per year?