CHAPTER 5

Mathematics of Individual Finance

[Mathematics of Individual Finance Page 1] [Time Value Of Money][Future Values] [More Frequent Compounding] [Effective Annual Interest Rate] [Present Value]
[Annuities] [Present Value Of An Annuity] [Annuities Due] [Future Value Of An Annuity] [Determining Payments] [Bond Valuation]
[Uneven Cash Flows] [Amortization Schedule] [Household Capital Budgeting] [Duration] [Summary] [Discussion Questions]
[Problems]

Future Value

All of this adds to the fact that a dollar tomorrow is worth more than a dollar today. Let's consider a dollar placed in a savings account at a bank which currently pays an annual percent rate (APR) of interest of 4%. To make this example simple, we will have the bank compound and pay interest annually. This means that the interest will be calculated and paid to your account exactly one year following your deposit.

In this simple example, the future value of your deposit at the end of one year is equal to the present value plus the interest. The interest is, of course, equal to the present value times the rate of interest, expressed as a percentage.

FV1 = PV0 + P

(Equation 5-1)

where FV1 is the future value at the end of the first period

PV0 is the present value of the amount being saved or invested

r is the rate of interest, expressed as a decimal.

In our simple illustration,

FV1 =$1 + $1(.04)
= $1 + $0.04

Note that we can also write Equation 5-1 in a slightly different (and more convenient) way by factoring the PV0's.

FV1 = PV0(1+r)

(Equation 5-2)

Therefore, in our example:

FV1= $1(1.04)
= $1.04

If the deposit is kept with the bank for 2 years at that same rate, the money compounds and earns interest on the interest as well as on your original principal of $1.

At the end of 2 years, an additional 4% will have been earned on the $1.04 which was in the account at the end of the first year, thereby giving us slightly more than an additional 4 cents in interest for the second year.

FV2= FV1 + FV1(r)
= $1.04 + $1.04(.04)
= $1.04 + $0.0416
= $1.0816

And since:

FV2 = FV1(1+r)

(Equation 5-3)

and from Equation 5-2:

FV1 = PV0(1+r)

then by combining Equations 5-2 and 5-3:

FV2= PV0(1+r)(1+r)
= PV0(1+r)2

(Equation 5-4)

And since the same principle is at work for three or more periods, we can rewrite Equation 5-4 for any number of periods which we can call n.

FVn = PV0(1+r)n

(Equation 5-5)

This says that the future value of an amount of money in the present may be found by multiplying the amount of money by the future value interest factor equal to 1 plus the rate of interest (in decimal format) raised to the power n. The future value interest factor may be found in Table A-3 in the Appendix to this book. Note that in these tables, the rate of interest is expressed as k rather than r. If you look up the future value interest factor for 2 periods and 4%, it is 1.0816 which you would expect.

On most financial calculators, the percent interest button says "%i." To arrive at the future value of $1 for 2 years at 4%, enter 2 for N, 4 for %i (note that most calculators require that interest be entered in percent rather than decimal form without the decimal point) and 1 for PV (present value). Then hit the compute button (often "CPT") followed by FV (future value). The answer should be 1.0816.

If you are using a LOTUS spreadsheet, place the amount of the present value ($1) in a cell and move to an empty cell in which we will calculate the future value. Note that LOTUS will not allow you to use the @FV function to calculate the future value of an amount, it is used only for annuities which we will learn later in the chapter. However, we can reproduce Equation 5-5 by multiplying the present value by (1+r)n. LOTUS uses the caret ^ to represent an exponential power. Therefore, the LOTUS formula for the future value of a sum of money would be (PV)*(1+r)^n. If the present value was $1 and this amount was placed in cell B2, the formula (in any empty cell) for the future value at 4% in 2 years would be (B2)*(1.04^2) and will equal 1.0816.

Example 5-1

Cindy buys a 6 year bank certificate of deposit (CD) which pays an annual rate of interest of 5%. If she puts $3,850 in the CD, how much will she have when it matures?

Solution 5-1

FV6= PV0(1+r)6
= $3,850(1.05)6
= $3,850(1.3401)
= $5,159.39

If you use the tables, you will note that the future value interest factor is 1.3401 and you will come out with the same answer. If you use the finance calculator, [2 N 5 %i 3850 PV CPT FV] you will come up with a slightly lower number, $5,159.37 (rounded to 2 decimal places) because of rounding errors. On LOTUS the formula would be (3850)*(1.05)^6 and you will reach the same answer as the calculator.

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