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Amortizations

In this topic we detail how amortization is related to the present value of an ordinary annuity and we determine ways to (a) find the unpaid balance of a loan, (b) find the borrowing amount with a budget in mind, and (c) find the number of payments left needed to repay the loan.

Definition (Amortization) The process of repaying a loan that is to be repaid by a series of partial payments with interest charged on the unpaid balance at the end of each period is called amortization. If the debt of amortizations _gr_1.gif] dollars, with interest rate amortizations _gr_2.gif] per period, is amortized by amortizations _gr_3.gif] equal periodic payments, the size of each payment is given by the formula

amortizations _gr_4.gif]   

Example (Amortization) (a) A loan of $10,000 is to be amortized with 10 equal  quarterly payments. If the interest rate is 6%, compounded quarterly, what is the periodic payment?
    The payment is given by the formula amortizations _gr_5.gif] where amortizations _gr_6.gif] amortizations _gr_7.gif] amortizations _gr_8.gif] and amortizations _gr_9.gif] We have amortizations _gr_10.gif] amortizations _gr_11.gif]
    (b) A woman buys a car for $15,000. If the interest rate on the loan is 12%, compounded monthly, and if she wants to make monthly payments of $500 for 3 years, how much must she have for a down payment?
    She wants the payment to be $500 which is given by the formula amortizations _gr_12.gif] where amortizations _gr_13.gif] amortizations _gr_14.gif] and amortizations _gr_15.gif] amortizations _gr_16.gif] We have

amortizations _gr_17.gif]

amortizations _gr_18.gif]

amortizations _gr_19.gif]

Therefore, no down payment is needed. amortizations _gr_20.gif]

Definition (Amortization Schedule) A table of values that reconstructs all the information of a loan that has been amortized is called an amortization schedule.

Example (Amortization Schedule) Develop an amortization schedule for a loan of $50,000 with interest at 10%, compounded semiannually, if it is to be repaid in amortizations _gr_21.gif] years by making equal semiannual payments.
    The amortization is amortizations _gr_22.gif] amortizations _gr_23.gif] amortizations _gr_24.gif] amortizations _gr_25.gif] and the payments are amortizations _gr_26.gif] amortizations _gr_27.gif] Therefore the schedule is:
    
amortizations _gr_28.gif]

amortizations _gr_29.gif]    

Definition (Unpaid Balance) For a loan of amortizations _gr_30.gif] payments of amortizations _gr_31.gif] dollars per period at interest rate amortizations _gr_32.gif] per period, the unpaid balance amortizations _gr_33.gif] after amortizations _gr_34.gif] payments have been made is given by the formula,

amortizations _gr_35.gif]

Example (Unpaid Balance) Find the unpaid balance after 15 payments for a $150,000 loan that has been amortized at 12%, compounded quarterly, and has quarterly payments of  $6489.36 for 10 years.
    The unpaid balance is given by the formula   amortizations _gr_36.gif] where amortizations _gr_37.gif] amortizations _gr_38.gif] amortizations _gr_39.gif] amortizations _gr_40.gif] and amortizations _gr_41.gif] We have

amortizations _gr_42.gif]
amortizations _gr_43.gif]

Example (Using Amortization) A couple purchasing a home wants their payment to be $500 per month. If they have $15,000 available for a down payment, and if the mortage rate on a 25-year loan is 12%, compounded monthly, how much can they spend on a house?
    Each payment is $500 and is given by the formula amortizations _gr_44.gif] where amortizations _gr_45.gif] amortizations _gr_46.gif] and amortizations _gr_47.gif] amortizations _gr_48.gif] so we have

amortizations _gr_49.gif]

amortizations _gr_50.gif]

amortizations _gr_51.gif]

So they can spend amortizations _gr_52.gif] amortizations _gr_53.gif] amortizations _gr_54.gif]
    

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Cite this as:
Amortizations
Published by Library of Math -- Online math organized by subject into topics.
Written by Smith, David A.
http://www.libraryofmath.com/amortizations.html
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