Humbly, I return to the Gods: HP12c Help!


Hey everyone, i hope your week is off to a good start.

Quick question, been reading up on the HP12c manual from the last series of posts but again i've arrived at a bump in the road.

Different interest periods and conversion periods.

ex. You are saving for a sail boat, and you deposit 1000 every three months into a bank account which pays 8%, compounded annually. Find the amount you will have saved at the end of five years.

This is the formula way but how is this done with the HP12c?

i=.08 (Compounded Annually)
n= 4x5=20

Anc= ----------------------------

Anc = 1000(24.15910964599272)
Anc= $24,159.10964599272

I can't find the little step to either change the Interest to an effective rate ( i think that is what it is, so it's quarterly like the payments) or just input the above info and let it do its magic.

Again, you scholars are again adding to my education, thank you.




The trick is to calculate the "effective payment" per compunding interval.

This is

[ PMT x ( N + I% x ( N + 1 )/2 ] / ( 1 + I% )

when the first payment is made at the beginning of a month and

[ PMT x ( N + I% x ( N - 1 )/2 ] / ( 1 + I% )

when the first payment is made at the end of the month

where N ist the number of payments per interval.

This is not part of any financial calculator. The reason is that you won't get any interest at all for payments made inside an compounding interval in the US.

Hope I got you right ^^

Of course, you can easily enter a program into your 12C



Yes, thank you for the knowledgeable explanation... (calculating the "effective") after learning this long hand, i wanted to just tap a few buttons on the HP12c and arrive at the same answer.

I have to take the time to learn how to program it... but for now i have to push forward and get this part of the MBA finished.

A million thanks... i'll be back i am sure.



This is not part of any financial calculator.

But the TI calculator's TVM solver can have non-equal payment periods and compounding periods (along with my TVM solver I posted a few weeks ago). While they may not be the best "Financial Calculator" around, they certainly have a nice TVM solver.


Years ago I tried a BA simulator on my PDA and it failed to calculate it correctly. I have to check this again. Thanks for pointing this out!


Use the nominal rate. You want to use the nominal rate P quarterly which gives an annual effective rate of 8%. I would imagine the 12c has an effective <--> nominal conversion ability. If not, here's the conversion by hand:

(1+P/4)^4 = 1.08

Solve for P (4th root; subtract 1; multiply by 4). This gives


Use that in the 12c finance solver along with 4 compoundings, and you should get the correct answer.



HP has provided quite a few learning modules on their webpages just to help with problems like this.

One in particular:

Interest Rate Conversions

is exactly what you need to do for this problem.

The basic answer is: The 12c and 12cp are "per period" calculators, where the interest rate is always given per period. A period in this case is the payment period. Monthly payments require a monthly interest rate. If the interest rate is annual, you must convert it to the equivalent monthly interest rate and use that.

Formula: Effective rate = ( ( 1 + nominal rate / periods per yr ) ^ (periods per year) ) - 1

In your example, you woudl be going backward from an effective rate to the nominal rate compounded more than once a year.

The learning module shows how to do that.

Some calculators (17b2, 10b2 and some TI models) allow for different compounding periods for interest rates compared to payment periods. The HP 12c does not. It is/was a design decision. Much of the financial world would be very upset :-) if someone changed how the 12c works.

Here is the link to all the learning modules for the 25th anniversary HP 12c in one zip file.

2.7MB Zip file of all HP learning modules for the 12cp



Wow... I'm flying through this current course with the added insight from everyone here and all the extra modules.

Everyone... thank you for the quick replies.

As i've mentioned before is there anything i can do for this forum? Perhaps keep my eye out for rare calculators i see in stores around the area? Lots of banks from the 70'and 80's down here... i bet there are boxes full of antique HP's etc.




down here]

Where is "here"? Maybe you can host the next calculator conference and we will all come visit - like next January or February!


Where is "here"? Maybe you can host the next calculator conference and we will all come visit - like next January or February!

I am in the French West Indies.. Martinique! Beautiful island... beaches, a family i am friends with own the old hilton, the hotel bateliere here and the club med. Is that good enough to host a conference?

Sorry, took a bit to reply to that one!!!

Doors are open down here... you all will get me through my MBA with all your help... i'll host it every year in a new country.


4 [n] 1 [CHS] [PV] 0 [PMT] 1.08 [FV] [i] ->1.94%, the effective rate per quarter


[g] [END],

20[n] 0 [PV] 1000 [CHS] [PMT] [FV] -> $24,159.11



... great!

-- Antonio


Lol.. that slick little method of getting the effective rate just cut my project time in half. As i stated in the Title of this post... "... Gods"

4 [n] 1 [CHS] [PV] 0 [PMT] 1.08 [FV] [i] ->1.94%, the effective rate per quarter

It's just that easy, isn't.

Great work.



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