The Museum of HP Calculators

# Loan Repayment for the HP-65

This program is Copyright © 1974 by Hewlett-Packard and is used here by permission. This program was originally published in the HP-65 Standard Pac.

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.

 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.

or

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  yx
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
```