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Software Vault: The Diamond Collection
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The Diamond Collection (Software Vault)(Digital Impact).ISO
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carbs20.zip
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FINANCE.TXT
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1995-01-15
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Interest-ing Finance
A certain dictionary I use defines interest as 'A sum
charged for borrowed money.' Having given the subject
this exhaustive treatment, it moves on to other matters.
Well, after all, it is not the province of the dictionary
to teach finance, so here is what they call in the
boardroom a 'broad brush' treatment of the subject for
those of you who want to approach your financial
education gradually.
The amount of interest a borrower pays depends on a
number of things:
- The amount borrowed (Principal)
- The term, or time in months or years taken to
repay the loan
- The number and frequency of payments
- The interest rate, also known as the Annual
Percentage Rate or APR.
- The method used to calculate the interest
The simplest form of interest is called, as you might
suspect, Simple Interest. Most types of loans use some
variation of simple interest. Compound interest pertains
more to deposit accounts, and will not be considered
here.
The easiest loan to calculate is one which is paid
back in a single payment at the end of a year. If the
amount borrowed is $ 1000 and the APR is 10%, for
example, the amount of interest due at the end of the
year is $ 100, and the total due is $1100.
Another type is called a Discounted Loan. The lender
calculates the interest and deducts it from the
principal. In other words the borrower receives the face
amount less the interest. The payments are calculated by
dividing the total, interest + principal, by the number
of payment periods. Here is an example of the
calculation:
The principal is $5000 and the annual interest rate
is stated as 10%. Ten percent of $5000 is $500. $5000
minus $500 is $4500 which is the amount received by the
borrower, who pays $500 for the use of it. 500 divided by
4500 is 11.1% The interest rate is already above the
stated rate. If the loan is paid back during the year
in more than one payment, the actual rate, as compared
to the stated rate, goes higher. Because part of the
money was used less than a full year.
Another form of loan, calculates the interest and adds
it to the principal. This is now the face amount on which
the interest is calculated. This is called, for obvious
reasons, Add-On interest.
Suppose you want to borrow $ 5000 at 10%. The lender
calculates 10% of $ 5000, which is $ 500, and adds the
500 to the 5000, equalling $ 5,500. This is the new face
value of the loan on which the interest is calculated.
Taking 10% of $ 5,500 we get $ 550, the interest charged.
You get $ 5000 and for this you pay $ 550. Divide it out
and it comes to 11% if paid off at the end of a year in
one payment. If paid before the end of a year, or paid in
installments, the actual interest rate is higher.
* * *
When the Discounted or Add-On type of loan is repaid
in monthly installments, some lenders will rebate part of
the interest if the loan is paid off early. The method
most frequently used to determine the amount is called
the Rule of 78's. There is a program on this disk
named Rule78 which figures the percentage of the interest
money to rebate, determined by the month in which the
payoff is made. The percentage of the rebate is
calculated as follows:
The sum of the digits from 1 to the number of payments
remaining, divided by the sum of the digits from 1 to
total number of payments specified in the loan documents.
$ 1000 is borrowed for one year at 10% interest, and is
to be repaid in 12 monthly payments. If the loan is paid
off after the 6th payment....
12 - 6 = 6 (number of payments remaining)
(1+2+3+4+5+6) = 21
(1=2=3=4=5=6=7=8=9=10=11=12) = 78
21 divided by 78 = 26.92%
Total interest for full term would be $100 (10 percent of
1000)
Rule78 calculates that 26.92 percent of the interest
charge should be rebated if payoff occurs after sixth
payment is made.
Rebate of Interest if loan is paid off after 6th payment
would be 26.92 percent of $100, or $26.92
* * *
The most common type of loan is one where the
repayment is done in equal monthly installments, in which
each monthly payment includes one month's interest on the
balance remaining unpaid. This is called a Declining
Balance or Amortized loan. It is the kind of loan you
probably have on your car or mortgage.
The amortized loan is the hardest to calculate. For
example, you borrow five thousand dollars to buy a used
car, and have three years to pay it back. Your first
payment must contain enough money to pay the interest on
the entire principal for a month, plus an additional
amount to pay back part of the principal. Subsequent
payments consist of interest for one month on the unpaid
balance, plus payment of part of the principal. With each
succeeding payment the interest portion will be less than
it was the previous month and the amount paid toward the
principal will be more, because the unpaid balance is
less each time. Yet the total of each monthly payment,
interest plus principal, must be the same as it was the
first month. Over the course of the loan It must all work
out very neatly so that, at the end of 3 years, the loan
has been paid off in equal monthly payments. Can it
really be possible to figure out a way to do this?
Fortunately for people like you and me, a formula was
devised years ago, and here it is, as used by most banks
to this day:
Monthly Payment = PV x (I/(1-(1+I)))^ -N
PV (Present Value) - Is the amount of money borrowed.
I - Is the monthly interest rate as a decimal. (The
annual rate divided by 1200, i.e., by 100 to change it
from a percent to a decimal, and by 12 to change it from
from yearly to monthly.)
N - Is the number of months for which the money is
borrowed.
^-N means raised to the power of -N
Do not try to work this out in your head. You may end
up with a sprained brain. A few of you may be able to
figure the monthly payment on your loan with a calculator
using this formula. However, since you own a personal
computer, there are many good programs available which
figure out the monthly payment, and make a printout by
month showing interest per payment, principal per
payment, balance to maturity, and amount due if the loan
is fully paid before maturity. (That which the banks and
car dealers call the Payoff.) One such program, HIFI, is
included with the CAR BS program.
This last, the Payoff, is simply the amount borrowed
minus the total of the principal paid to date. If you
plan to pay off ANY loan before maturity, it is best to
call the bank before you write the check, and ask for the
amount due, as there may be other charges involved.
From the discussion of amortized loans you may have
been able to infer that most of the interest is paid
early in the life of the loan when the principal is
largest. This makes it hardly worth while, for example,
to pay off a six year loan in year five when the
remaining interest may be negligible.
A final word on the amortized loan equation. You may
sometimes see it in a more complicated form than shown
here. You will find that the longer equation accommodates
a Balloon Payment. Some lenders make the last payment
larger than the others, thus name. The object is to make
the monthly payments lower. The balloon payment is
usually a large one, and the optimistic borrower assumes
it will be easier to pay in the future than in the
present. This type of thinking is occasionally seen today
in certain types of home mortgages where payments start
out small and get larger as time passes.
* * *
If you are still with me, let me congratulate you.
You now know enough about loans and interest to be
dangerous.
End