HP Prime: Car
Payment and Affordability
Introduction
The two programs presented here tackle common financial
questions of purchasing automobiles. (or
other equipment). CARPMT calculates
what would be the monthly payment, while CARAFFORD calculates the sticker price
that the buyer can afford. The variables
that are considered are:
N = number of monthly payments, typically 48, 60, or 72 (for
4, 5, or 6 year term, respectively)
I = annual interest rate of the buyer can get, hopefully
this rate is low
S = sales tax rate
D = discount rate, as car dealers tend to off discounts
W = down payment (enter as negative)
Firmware 13441 is used and the Finance app functions TvmPMT
and TvmPV are used. For the finance
functions, they are designated with the “Finance.” prefix to allow usage of the
program on any app. TVM cash flow
convention is retained, outflows (payments) are entered as negative while
inflows (in this case the financing loan) are treated as positive.
HP Prime Program CARPMT
EXPORT CARPMT(N,I,P,S,D,W)
BEGIN
// enter down pmt as negative
// 2018-03-12 EWS
// Function Setup
// no. payments,
// annual interest, price,
// sales tax, discount, down pmt
LOCAL X;
X:=P*(1+S/100)*(1-D/100)+W;
// Finance app
X:=
Finance.TvmPMT(N,I,X,0,12);
RETURN ROUND(X,2);
END;
Example:
Term: 60 months
Interest Rate: 4.5%
Sticker Price: 18995
Sales Tax: 9.5%
Discount Rate: 10%
Down Payment: $1000
CARPMT(60,4.5,18995,9.5,10,-1000)
Result: -330.35
Payment is $330.35
HP Prime Program CARAFFORD
EXPORT CARAFFORD(N,I,X,S,D,W)
BEGIN
// pmt and down pmt enter
// as negative
// 2018-03-12 EWS
// Function Setup
// no pmts, annual interest,
// payment (as pqsitive),
// sales tax, discount, down pmt
LOCAL P;
// Finance app
P:=
Finance.TvmPV(N,I,X,0,12);
// calculating affordable price
P:=(P-W)/((1+S/100)*(1-D/100));
RETURN ROUND(P,2);
END;
Example:
Term: 60 months
Interest Rate: 4.8%
Payment: $350.00
Sales Tax: 9.5%
Discount Rate: 10%
Down Payment: $500
CARAFFORD(60,4.8,-350,9.5,10,-500)
Result: $19,418.67
The car that can be afforded is $19,418.67 (before sales tax
and discounts).
As day of this post is on Pi-Day Eve, Happy Pi Day on
March 14! π = 3.141592653…
Eddie
This blog is property of Edward Shore
