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Two Methods Prospective method:
outstanding principal at any point in time is equal to the present value at that date of all remaining payments
Retrospective method:outstanding principal is equal to the original principal accumulated to that point in time minus the accumulated value of all payments previously made
Note: of course, this two methods are equivalent. However, sometimes one is more convenient than the other
Examples
• (prospective) A loan is being paid off with payments of 500 at the end of each year for the next 10 years. If i = .14, find the outstanding principal, P, immediately after the payment at the end of year 6.
• (retrospective) A 7000 loan is being paid of with payments of 1000 at the end of each year for as long as necessary, plus a smaller payment one year after the last regular payment. If i = 0.11 and the first payment is due one year after the loan is taken out, find the outstanding principal, P, immediately after the 9th payment.
Formulas
PntpymtI paid *
nr
nr
pymtnrP
nt
nt 111
Simple Interest Amortized Loan Formula
Interest Paid
Formulas
nr
nr
pymtnrP
nT
nT 111balanceunpaid
Unpaid Balance Formula
T is the number of years from the beginning of the loan to the present
AMORTIZATION SCHEDULE• GOAL: DIVIDE EACH PAYMENT (OF ANNUITY) INTO TWO PARTS – INTEREST
AND PRINCIPAL• AMORTIZATION SCHEDULE – TABLE, CONTAINING THE FOLLOWING COLUMNS:
• PAYMENTS• INTEREST PART OF A PAYMENT• PRINCIPAL PART OF A PAYMENT• OUTSTANDING PRINCIPAL
Duration Payment Interest PrincipalRepaid
Outstanding Principal
0 5000.00
1 13875.05 600.00 787.05 4212.95
2 13875.05 505.55 881.50 3331.45
3 13875.05 399.77 987.28 2344.17
4 13875.05 281.30 1105.75 1238.42
5 13875.05 148.61 1238.44 0
Example:5000
at 12 % per yearrepaid by 5 annual
payments
Amortization schedule:
Example
t - 1 t
PaymentX
Outstanding principal
P Interest earned during interval (t-1,t) is iP Therefore interest portion of payment X is iP and principal portion is X - iP
A 1000 loan is repaid by annual payments of 150, plus a smaller final payment. If i = .11, and the first payment is made one year after the time of the loan, find the amount of principal and interest contained in the third payment
Recall: in practical problems, the outstanding principal P can be found by prospective or retrospective methods
Amortization Schedule Steps:
• Find the interest on amount use – Use the simple interest formula.
• Principal portion is payment minus interest portion.
• New balance is previous balance minus principal portion.
For the last period • Principal portion is previous balance. • Total payment is sum of principal portion and
interest portion.
Amortization Schedule Steps:
Payment Number
Principal Portion
Interest Portion
Total Payment
Balance
0 --------- --------- --------- loan amount
first through
next-to-last
total payment
minus interest portion
simple interest on previous balanceI = Prt
use simple interest
amortized loan
formula
previous balance
minus this payment’s principal portion
last previous balance
simple interest on previous balanceI = Prt
principal portion plus
interest portion
$0.00