HP Program Mortgage calculator

Mortgage program for HP28S
Mortgage program for HP28S

HP Program Mortgage calculator Formula

The HP program mortgage calculator uses the following formula to calculate the mortgage payments:
Payment = Price / [(1/I) – 1/{I*(1+I)^n}]
I = Interest per month = yearly Interest / 12
n = number of month

Before you start, create a directory

First make sure you are at HOME or root directory. You do that by doing the following:
Press MEMORY or shift-I then HOME then the USER button
Create a directory by pressing ‘House then MEMORY or shift-I then CRDIR
Here you can save your program and helper code.

Helper programs

If you want to run this program after some time again it might be hard to remember what to do. So I created a quick Instruction set. There are 2 helper functions.
CLR with erase all variables used during the calculations
ANLEI will show what to add on the screen before running the program
HPAY is the program
UP is a function/program to go one sub menu up

Helper programs
Helper programs

Input for the program

Execute the program ANLEI it will display the following
PRICE, DOWN%, INT%, YEAR
so the sales price of the property is 500000, the down payment is 5%, the yearly interest rate is 4% and the loan is for 30 years

Input parameter for mortgage program
Input parameter for mortgage program

Program output

After starting the program HPAY it will output the following
IMO if pressed will display the monthly interest (just used for calcs)
PMI will display the monthly mortgage insurance payments of 0.34% if your down payment is less then 20%
L is the balance of the Loan after your down payments
TAX is the monthly property tax you which needs to be paid yearly
So based on the input above the monthly mortgage is 2267.72
Note: Before starting a new calculation press the CLR menu button which will erase all variables.

HP mortgage program output
HP mortgage program output
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