The Museum of HP Calculators

HP Forum Archive 17

 formulaMessage #1 Posted by stafford on 21 Oct 2007, 1:44 a.m. Would someone show me the formula(s) for these financial calculations so I can put them in a math program! Such as.. how to solve for each one of these given the value of the others Present Value = Future Value = Interest Rate = Term = Payment = Thanks in advance :)

 Re: formulaMessage #2 Posted by Allen on 21 Oct 2007, 2:00 a.m.,in response to message #1 by stafford May I recommend that you google present value formula first. There are plenty of articles with these formulas already posted, all of them are very easy to find, no need to re-type them all here or ask for help. Edited: 21 Oct 2007, 2:03 a.m.

 Re: formulaMessage #3 Posted by Namir on 21 Oct 2007, 9:31 a.m.,in response to message #1 by stafford You need the manual for the HP-12C. It answers all your questions. The manual has an appendix containing all the financial formulas regarding present value, future values, periodic payments, and so on. Namir

 Re: formulaMessage #4 Posted by Chris McCormack on 21 Oct 2007, 2:44 p.m.,in response to message #1 by stafford Quote: Would someone show me the formula(s) for these financial calculations so I can put them in a math program! Such as.. how to solve for each one of these given the value of the others : Present Value, Future Value, Interest Rate, Term, Payment Thanks in advance :) I've had this program sitting in my HP15C for a long time now. I've also used close relatives on the HP11C and HP33S. Not as fancy as some of the TVM programs people use, but nice to have ready when trying to talk turkey at a car dealership! ```Time Value of Money Calculations for HP-15C Chris McCormack - 21 Oct 2007 These routine perform loan calculations using the present value annuity factor, or PVAF. This relates the present value (loan amount) to the periodic payments necessary to pay it off. PVAF(r,N) = (1/r)[1-1/(1+r)^N] In this equation, r is the decimal interest per payment period (.01 would represent a monthly loan with a 12% rate) and N in the number of payments (48 would work for a four-year car loan). Note - Labels 9 and 6 were used because 9 is next to the divide key (breaking the loan down into payments) and 6 is next to the multiply key (building up the total loan amount). Memory Usage: 21 steps Register usage: R0 = interest rate per period R1 = number of periods Label Usage: LBL 9 : calculate payment for a given amount borrowed LBL 6 : calculate amount borrowed for a given payment LBL.9 : (internal) determine PVAF 001 LBL 9 // ( LoanAmt -- Payment ) 002 GSB .9 / // divide PV by PVAF 004 RTN 005 LBL 6 // ( Payment -- LoanAmt ) 006 GSB .9 * // multiply payment by PVAF 008 RTN 009 LBL .9 // ( -- PFAV ) 010 RCL 0 1 + // R0 holds interest per period 013 RCL 1 CHS y^x // R1 holds number of periods 016 1 x<>y - 019 RCL 0 / 021 RTN Sample calculations: \$5000 borrowed at 10% with 36 monthly payments --> \$161.34 / month \$1500/month on a 30 year mortgage at 7.5% --> \$215,526.44 borrowed ```

 Re: formulaMessage #5 Posted by Chuck on 22 Oct 2007, 12:35 a.m.,in response to message #1 by stafford Here's the one I have memorized. The first part is the compound interest formula; the second is an ordinary annuity formula. Usually you set them equal to each other for annuities, loan payments, sinking funds, etc. Taking the difference gives you the balance on a loan, or set it to 0 for the above calculations. ``` nt nt (1 + r/n) - 1 P(1 + r/n) - Pmt -------------- = bal r/n P = principal n = compoundings (or payments) per year t = time in years r = annual interest rates pmt = periodic payment bal = balance ``` This formula resides in most of my HP's.

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