HP 12C and HP Prime:
Combo Loans
Introduction
Home buyers with good credit are sometimes offered a combo
loan, also known as a “Piggyback” loan, as a financing option in purchasing the
house. When more than the amount of a
purchase of a home is above 80% of the purchase price, private mortgage
insurance (PMI) is required. In order to
save money, combo loans split the price into multiple loans. Common types include:
80:20: Two loans, one
for 80% of the price (large), 20% of the price (small)
80:15:5: Two loans,
one for 80% of the price (large), 15% of the price (small), with 5% of the
price as a down payment
80:10:10: Two loans,
one for 80% of the price (large), 10% of the price (small), with 10% of the
price as a down payment
Each loans have separate terms (number of years and interest
rate). Monthly end-of-period payments
are assumed.
HP Prime Program
COMBOLOAN
The program COMBOLOAN calculates the payments for both
separate loans and combined loans. This
particular loan covers of three types:
80:20, 80:15:5, and 80:10:10.
EXPORT COMBOLOAN()
BEGIN
// EWS 2018-04-05
// Piggyback Loan
LOCAL a,lst,k;
LOCAL t1,t2,i1,i2;
LOCAL d,p1,p2,p;
// terms, order allows to
// use eqn −5*k+25
lst:={"80:20","80:15:5","80:10:10"};
// input
INPUT({a,t1,i1,t2,i2,{k,lst}},
"Payment: Combo Loan",
{"Loan:
","Term1:","Rate1:",
"Term2:","Rate2:","Type
:"},
{"","years","","years","",""});
// calculation
p1:=Finance.TvmPMT(t1*12,i1,a*0.8,0,12);
p2:=Finance.TvmPMT(t2*12,i2,a*(−0.05*k+0.25),0,12);
p:=p1+p2;
// down payment
d:=−a*0.05*(k-1);
// payment: down, total,
// large, small
RETURN {d,p,p1,p2};
END;
Output: {down
payment, total payment, large payment, small payment}
Examples:
Loan Amount:
$200,000.00
80% Loan: Term: 30
years, Rate: 4.5%
Small Loan: Term: 15 years, Rate 5%
Example 1: Type 80:20
Result: {0,
-1,127.01, -810.70, -316.32}
Example 2: Type
80:15:5
Result: {-10,000.00, -1047.93, -810.70, -237.24}
Example 3: Type
80:10:10
Result: {-20,000.00,
-968.86, -810.70, -158.16}
HP 12C Platinum
Program: 80:10:10 Combo Loan
Inputs:
Store Loan Amount in R1
Large Loan (80%):
Number of Years in R2, Annual Interest Rate in R3
Small Loan (10%):
Number of Years in R4, Annual Interest Rate in R5
Output:
Large Loan Payment, Small Loan Payment, Combined Payment
(R6)
|
STEP
|
CODE
|
KEY
|
NOTES
|
|
001
|
42, 34
|
Clear FIN
|
|
|
002
|
45, 1
|
RCL 1
|
|
|
003
|
8
|
8
|
|
|
004
|
0
|
0
|
|
|
005
|
25
|
%
|
|
|
006
|
13
|
PV
|
|
|
007
|
45, 3
|
RCL 3
|
|
|
008
|
43, 12
|
[ g ] [ i ] (12÷)
|
Store monthly
interest rate
|
|
009
|
45, 2
|
RCL 2
|
|
|
010
|
43, 11
|
[ g ] [ n ] (12x)
|
Store monthly
payments
|
|
011
|
14
|
PMT
|
Calculate payment
of 80% loan
|
|
012
|
44, 6
|
STO 6
|
|
|
013
|
31
|
R/S
|
|
|
014
|
45, 1
|
RCL 1
|
|
|
015
|
1
|
1
|
|
|
016
|
0
|
0
|
|
|
017
|
25
|
%
|
|
|
018
|
13
|
ENTER
|
|
|
019
|
45, 5
|
RCL 5
|
|
|
020
|
43, 12
|
[ g ] [ i ] (12÷)
|
|
|
021
|
45, 4
|
RCL 4
|
|
|
022
|
43, 11
|
[ g ] [ n ] (12x)
|
|
|
023
|
14
|
PMT
|
Calculate payment
on the 10% loan
|
|
024
|
31
|
R/S
|
|
|
025
|
45, 6
|
RCL 6
|
|
|
026
|
40
|
+
|
|
|
027
|
44, 6
|
STO 6
|
|
|
028
|
43, 33, 000
|
GTO 000
|
On the regular HP
12C, the line is GTO 00
|
Example:
Terms: 80:10:10
Loan Amount: $200,000.00
80% Loan: Term: 30
years, Rate: 4.5%
10% Loan: Term: 15 years, Rate 5%
Results:
-810.70 (payment of
80% loan)
-158.16 (payment of
10% loan)
-968.86 (payment of
combined loan)
Sources
Calculated Industries Real Estate Master IIIX: Resident
Real Estate Finance Calculator Pocket Reference Guide Calculated Industries, LLC.: Carson City, NV 2010
Mortgage-Info.com
“Piggy Back Mortgage Calculator” Mortgage Info.com 2011 http://www.mortgage-info.com/mortgage-calculators/piggybackmortgagecalculator.aspx Accessed April 4, 2018.
Eddie
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