12c Solving for n

[Zac Bruce]

Hi all,

I'm hoping someone can lend their wisdom here. As most of you will well know, when using the 12c to solve for n, it will only solve as an integer, always rounding up. I tried to search but did not come across a solution.

The user manual offers the following solution for when a PMT amount is involved;
10.5 g i
35000 PV
325 CHS PMT
n (=328)

To find the partial last payment;
FV (181.89)
RCL PMT (-325)
+ (-143.11) which is the final fractional payment

To then make the answer correlate with other financial calculators I came up with the following;
(with the -143.11 still on screen)
RCL PMT X><Y %T (44.03) e.g. .4403 of a total payment.
So the answer is 327.44, which is what other calculators report.
This would be really simple to program, however it's simple enough to just remember or re-logic my way through


However, when a PMT value is not involved, I can't find a simple way of performing the same calculation. My math just isn't strong enough.
e.g. PV 1250, FV 2500, i=9% compounded annually, solve for n?
12c gives 9, and when you re-solve for FV it gives 2714.87
Other calculators will give n=8.04

Is there a simple way to calculate what the extra 214.87 represents in terms of time?
I have read that there was a program solution for this, but could not find it in part 3 of the manual or in the solutions handbook. If someone could point it out for me that would be greatly appreciated.

Many thanks,

Zac

EDIT to fix values.