Loan Repayment for the HP-65

This program is supplied without representation or warranty of any kind. Hewlett-Packard Company and The Museum of HP Calculators therefore assume no responsibility and shall have no liability, consequential or otherwise, of any kind arising from the use of this program material or any part thereof.

Card Labels
Loan Repayment
Label	Years ↑ per/year	i%	PV	PMT	Calc(P)
Key	A	B	C	D	E

Overview

Given the term for a direct reduction loan in years, the number of periodic payments per year, and the annual interest rate in percent this program computes:

1. Periodic payment amount, if the principal value borrowed is given.

2. The principal value if the periodic payment is given.

A one half cent round-off routine is incorporated so that the answers are correct to the nearest cent.

Formulas

PV = PMT * [ ( (1+i/(100*n))^yn-1 ) / ((i/(100*n))*(1+(i/100*n))^yn ) ]

where:

PV = Principal value
PMT= Periodic payment
i = Annual interest rate in percent
y = Number of years
n = Number of payment periods per year

Instructions

Step	Instructions	Input Data/Units	Keys	Output Data/Units
1	Enter program
2	Input number of years	y	ENTER↑	y
3	Input payment periods/year	n	A	yn
4	Input annual interest	i(%)	B	100
5	Input either principal value	PV	C	PV
	or payment	PMT	D	PMT
6	Calculate either
6	payment		E D	PMT
	or principal value		E C	PV
7	Perform steps 2 & 3, or step 4
8	or step 5 for new values.
	Note: Unrounded values for PMT or PV calculations are stored in register 8 after calculation

Example

Find the quarterly payment for a thirty year mortgage at 8.75% with a principal amount of $37,500. Key 30 and press Enter, then key 4 and press A to set up quarterly payments on a 30 year loan. Key in the interest rate of 8.75 and press B. Key 37500 and press C. To calculate the payment, press E and then D and the answer of 886.36 is displayed.

What principal value exactly corresponds to the payment just calculated? Press D to input the payment still in the x register. Press E and then C to calculate the exact principal of 37499.86.

What would the payment be if the interest rate was 9.25%? Key in 9.25 and press B. Press E and then D to calculate the new payment of 926.83.

At this new interest, what would the payments be if they were made monthly instead of quarterly? Key in 30 and press ENTER↑ and key 12 and press A to set up monthly payments. Then press E and then D to calculate the payment of 308.50.

The Program

 CODE  KEYS
   23  LBL
   11  A
33 07  STO 7
   71  ×
33 01  STO 1
   24  RTN 

   23  LBL 
   12  B
33 02  STO 2
   43  EEX 
   02  2
33 05  STO 5
   24  RTN 

   23  LBL 
   13  C
   32  f^-1
   71  SF 2 
   31  f 
   61  TF 1
   22  GTO 
   01  1
33 03  STO 3
   24  RTN
 
   23  LBL 
   14  D
   31  f
   61  TF 1 
   22  GTO 
   01  1
33 04  STO 4
   24  RTN 

   23  LBL 
   15  E
   31  f
   51  SF 1
   31  f
   71  SF 2
   24  RTN

   23  LBL
   01  1
   32  f^-1
   51  SF 1
34 02  RCL 2
34 07  RCL 7
   81  ÷
34 05  RCL 5
   81  ÷
   01  1 
   61  +
34 01  RCL 1
   35  g
   05  y^x
33 06  STO 6 
   01  1
   51  -
34 06  RCL 6 
   81  ÷
34 07  RCL 7 
   71  ×
34 02  RCL 2
   81  ÷
34 05  RCL 5
   71  ×
   32  f^-1
   81  TF 2
   22  GTO 
   03  3
34 03  RCL 3
35 07  g x⇔y
   81  ÷
   22  GTO
   04  4
   23  LBL
   03  3
34 04  RCL 4
   71  ×
   23  LBL
   04  4
33 08  STO 8
   21  DSP
   83  .
   02  2
34 05  RCL 5
   71  ×
   83  .
   05  5
   61  +
   31  f
   83  INT
34 05  RCL 5
   81  ÷
   84  R/S
35 01  g NOP
35 01  g NOP
35 01  g NOP
35 01  g NOP
35 01  g NOP
35 01  g NOP
35 01  g NOP
35 01  g NOP

Register Use

R1  yn
R2  i
R3  PV
R4  PMT
R5  100
R6  (1 + i/100)^yxn
R7  n
R8  PV or PMT

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