![]() The point is: there are two "exact" answers. periods of equal length, payments always made on either exactly the end or start of a period, all of which would effect real world accuracy. (07-25-2017 02:38 AM)Zac Bruce Wrote: Is it just beyond the capabilities of the calculator to give an exact answer? Or is further information needed? I know it works with certain assumptions e.g. Here is a short program that does these two calculations, depending on whether PMT=0 or not. The exact value can be calculated with the given formula: For instance, the PV for n=11 is not the mean of the PVs for 10 resp. Your approximate approach in effect calculates PV for n=327 (=34991,78) and n=328 (=35010,44) and then interpolates the "correct" n for PV=35000 between these two (your %T method is mathematically equivalent). The basic annuity formula for this case is I assume you mean the first problem here, the one with a given PMT. PMT=325 and not –325 due to the HP sign convention. Note: in the following formulas all values are unsigned, e.g. ![]() (07-25-2017 02:38 AM)Zac Bruce Wrote: Can you explain a little more about it being only an approximate answer? I even posted the steps to calculate n as a fractional result. You mean a solution for the PV=1250 and FV=2500 problem? There is a very simple solution. (07-25-2017 02:38 AM)Zac Bruce Wrote: I'm guessing that there is not a simple solution similar to the first problem. You can also enter n=8 and get the (lower) amount after 8 periods. OK, then this is the additional amount you get after full 9 periods. The second figure I meant 214.87 I.e the amount over what we expected or wanted. (07-25-2017 02:38 AM)Zac Bruce Wrote: It was late last night when I posted, so yes the figure you gave for the first question is correct and I have edited the post. What 714,87? I just see 2714,87 which is the FV after 9 periods. (07-24-2017 11:27 AM)Zac Bruce Wrote: Is there a simple way to calculate what the 714.87 represents in terms of time? ![]() For your example (no FV, "end" mode assumed) and i decimal (i.e. ) As shown, the PMT=0 case is trivial, but even with PMT the formula is quite simple. ![]() The formulas are known, so just "code your own". Of course you can always use your own little program for calculating n without rounding up to the next higher integer. If you really need the fractional answer for n this can be calculated directly, either manually or with a small program: (07-24-2017 11:27 AM)Zac Bruce Wrote: However, when a PMT value is not involved, I can't find a simple way of performing the same calculation. Anyway, at least you get an approximate result. Rounded to two decimals the difference in this particular case does not show up. ?!? Where do you get this 33,44 from? I'd say this is 327 full periods plus 0,4403 = 327,44 periods.īut this is only an approximate answer, it is a linear interpolation of a nonlinear function. So the answer is 33.44, which is what other calculators report. (07-24-2017 11:27 AM)Zac Bruce Wrote: To then make the answer correlate with other financial calculators I came up with the following Note: edited to address some more questions. If someone could point it out for me that would be greatly appreciated. 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. Is there a simple way to calculate what the extra 214.87 represents in terms of time? PV 1250, FV 2500, i=9% compounded annually, solve for n?ġ2c gives 9, and when you re-solve for FV it gives 2714.87 However, when a PMT value is not involved, I can't find a simple way of performing the same calculation. This would be really simple to program, however it's simple enough to just remember or re-logic my way through So the answer is 327.44, which is what other calculators report. To then make the answer correlate with other financial calculators I came up with the following + (-143.11) which is the final fractional payment ![]() The user manual offers the following solution for when a PMT amount is involved I tried to search but did not come across a solution. 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'm hoping someone can lend their wisdom here. ![]()
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