Hi, the initial condition presented above is incomplete. Is the 10% interest for one period (of 60 days) or is that the annual rate? So assuming the former, and assuming the loan amount is 5000, you have
P + I = -PMT(0.1/60, 60, 5000) = 87.64
total interest paid for the period = 60 * 87.64 - 5000 = 258.33
Total interest paid will not be 500. Because some principle is being returned everyday, the loan balance diminishes and thus the interest diminishes. However if all the 5000 principle was paid back on the last day, and not a bit every day, then interest would be 500.
You can use Pn = -PPMT(0.1/60, N, 60, 5000) to find out the amount of principle returned on day N. Interest paid on day N is P + I - Pn.
