Time Value of Money - Six Functions of a Dollar
Using Assessors’ Handbook Section 505 (Capitalization Formulas and Tables)
Appraisal Training: Self-Paced Online Learning Session

Lesson 2: Future Worth of $1
(Assessors’ Handbook 505, Column 1)

This lesson discusses the Future Worth of $1 (FW$1); one of six compound interest functions presented in Assessors’ Handbook Section 505 (AH 505), Capitalization Formulas and Tables. This lesson:

  • Explains the FW$1 function's meaning and purpose,
  • Provides the formula for FW$1 factors,
  • Contains practical examples of how to apply the FW$1 factor,
  • Explains the Rule of 72, and
  • Shows how to calculate the future value of multiple payments.

FW$1: Meaning and Purpose

The FW$1 is the amount to which $1 will grow at periodic interest rate i after n periods, assuming the payment of $1 occurs at the beginning of the first period.

The FW$1 is used to compound a single present amount to its future amount. The FW$1 factors are in column 1 of AH 505.

The future worth of 1 factor (FW$1) is based on the premise that $1 deposited at the beginning of a period earns interest during the period and becomes part of the principal at the beginning of the next period. This continues for the number of periods in the problem.



Formula for Calculating FW$1 Factors

The formula for the calculation of the FW$1 factors is

FW$1 = (1 + i)n

Where:

  • FW$1 = Future Worth of $1 Factor
  • i = Periodic Interest Rate, often expressed as an annual percentage rate
  • n = Number of Periods, often expressed in years

All of the other compound interest formulas published in AH 505 are derived from the basic compounding expression in the FW$1 factor, (1 + i)n. As we will see, this mathematical expression is the basic building block of all the other compound interest formulas.

The periodic interest rate, i, must match the compounding period, n (this holds for all compound interest functions). For example, if n is stated in years, indicating annual compounding, i must be stated as an annual rate; if n is stated in months, indicating monthly compounding, i must be stated as a monthly rate.

For now, we will assume annual compounding, so our periods, n, will be in years and the periodic interest rate, i, will be the annual percentage rate. Later, we will introduce the concept of more than one compounding period per year (monthly, quarterly, etc.).


In order to calculate the annual FW$1 factor for 4 years at an annual interest rate of 6%, use the formula below:

  • FW$1 = (1 + i)n
  • FW$1 = (1 + 0.06)4
  • FW$1 = (1.06)4
  • FW$1 = 1.262477


Viewed on a timeline:

Image of a timeline showing how a dollar deposited today at an annual interest rate of 6 percent with annual compounding would grow to $1.262477 after 4 years.

On the timeline, the initial deposit of $1 is shown as negative because from the point of view of a depositer it would be a cash outflow. The future value is shown as positive because it would be a cash inflow. The depositor gives up money now in order to receive money later.

To locate the FW$1 factor in AH 505, go to page 33 of AH 505. Go down 4 years and across to column 1. The FW$1 factor is 1.262477.

Image of a compound interest table (AH 505, page 33) highlighting the future worth of one  dollar factor for 4 years with annual compounding at an annual interest rate of 6 percent. The highlighted factor is 1.262477.

Link to AH 505, page 33

In most problems, we don’t want the FW$1; we want the future worth of some other amount that has been deposited or invested. To put it another way, we want to use the FW$1 factor to solve a TVM problem. When working problems, we will use the notation shown below. Don’t worry too much about the notation now. Using it will become easier as we work problems throughout the lessons.

Image showing abbreviations used for the six compound interest functions and related variables.
FW$1 stands for the future worth of $1 factor
PW$1 stands for the present worth of $1 factor
FW$1/P stands for the future worth of $1 per period factor
SFF stands for the sinking fund factor
PW$1/P stands for the present worth of $1 per period factor
PR stands for the periodic repayment factor
PV stands for the present value of a single amount or annuity
FV stands for the future value of a single amount or annuity
i stands for the periodic interest rate
n stands for the number of periods
PMT stands for the periodic payment



Practical Applications of FW$1

Example 1:
You deposit $2,000 today at an annual interest rate of 6%. How much will you have at the end of 10 years, assuming annual compounding?

Solution:

  • FV = PV × FW$1 (6%, 10 yrs, annual)
  • FV = $2,000 × 1.790848
  • FV = $3,582
  • Find the annual FW$1 factor (annual compounding) for 6% at a term of 10 years. In AH 505, page 33, go down 10 years and across to column 1 to find the correct factor of 1.790848.
  • The future value of $3,582 is equal to the present value of $2,000 multiplied by the factor.
Image of a compound interest table (AH 505, page 33) highlighting the future worth of one dollar factor for 10 years with annual compounding at an annual interest rate of 6 percent. The highlighted factor is 1.790848

Link to AH 505, page 33



Example 2:
The Jones family places $100,000 in an investment that will provide an annual rate of return of 5%. What will the investment be worth in 2 years?

Solution:

  • FV = PV × FW$1 (5%, 2 yrs, annual)
  • FV = $100,000 × 1.102500
  • FV = $110,250
  • Find the annual FW$1 factor (annual compounding) for 5% at a term of 2 years. In AH 505, page 29, go down 2 years and across to column 1 to find the correct factor of 1.102500.
  • The future value of $110,250 is equal to the present value of $100,000 multiplied by the factor.
Image of a compound interest table (AH 505, page 29) highlighting the future worth of one dollar factor for 2 years with annual compounding at an annual interest rate of 5 percent. The highlighted factor is 1.102500.

Link to AH 505, page 29



Example 3:
You have $450,000 to invest and can earn an annual interest rate of 7.50%. How much will your investment be worth in 10 years?

Solution:

  • FV = PV × FW$1 (7.50%, 10 yrs, annual)
  • FV = $450,000 × 2.061032
  • FV = $927,464
  • Find the annual FW$1 factor (annual compounding) for 7.50% at a term of 10 years. In AH 505, page 39, go down 10 years and across to column 1 to find the correct factor of 2.061032.
  • The future value of $927,464 is equal to the present value of $450,000 multiplied by the factor.
Image of a compound interest table (AH 505, page 39) highlighting the future worth of one dollar factor for 10 years with annual compounding at an annual interest rate of 7.50 percent. The highlighted factor is 2.061032.

Link to AH 505, page 39



Example 4:
A given product costs $500 today. The cost of the product is expected to rise at an annual rate of 10%. How much will the product cost in 5 years?

Solution:

  • FV = PV × FW$1 (10%, 5 yrs, annual)
  • FV = $500 × 1.610510
  • FV = $805
  • Find the annual FW$1 factor (annual compounding) for 10% at a term of 5 years. In AH 505, page 49, go down 5 years and across to column 1 to find the correct factor of 1.610510.
  • The future value of $805 is equal to the present value of $500 multiplied by the factor.
Image of a compound interest table (AH 505, page 49) highlighting the future worth of one dollar factor for 5 years with annual compounding at an annual interest rate of 10 percent. The highlighted factor is 1.610510.

Link to AH 505, page 49



Example 5:
Approximately how long does it take a given amount to grow to 10 times its original amount, given an annual interest rate of 5% with annual compounding?

Solution:

  • Use the compound interest tables to estimate the answer by inspecting the tables.
  • On the annual page for 5% (AH 505, page 29), inspect the FW$1 column (column 1) to find a factor that is approximately equal to 10 (FV ÷ PV = 10 ÷ 1).
  • The answer is slightly greater than 47 years (the factor for 47 years is 9.905971).
Image of a compound interest table (AH 505, page 29) highlighting the future worth of one dollar factor for 47 years with annual compounding at an annual interest rate of 5 percent. The highlighted factor is 9.905971.

Link to AH 505, page 29



“Rule of 72”

The Rule of 72 is a rule of thumb that is closely related to the FW$1 factor. The rule assumes annual compounding.

The Rule of 72 can be used to estimate either of the following:

  1. The number of years it would take for an amount to double at a given annual interest rate, or
  2. The annual interest rate, if an amount has doubled in a given number of years.


The formula for the Rule of 72 is:

Image showing the formula for the Rule of 72. The number of years for an amount to double is equal to 72 divided by the annual interest rate.

Or, transposing:

Image showing the transpose of the formula for the Rule of 72.  The annual interest rate is equal to 72 divided by the number of years for an amount to double.

(Note: When using the Rule of 72, the annual interest rates are stated as percentages, not as decimals.)

The smaller the difference between the factors of 72 (i.e., the number of years and the annual interest rate) the more accurate the estimate. For example, when the factors are 9 and 8, the estimate is more accurate than when the factors are 36 and 2.



Practical Applications of “Rule of 72”

Example 1:
You deposit $1,000 in an account that pays an annual interest rate of 6%. Approximately how long will it take this deposit to grow to $2,000?

Solution:
Image showing the formula for the Rule of 72.  The number of years for the amount to double is equal to 72 divided by the annual interest rate, in this example, 72 divided by 6, which equals 12 years.

The estimate may be confirmed using the compound interest tables in AH 505, page 33, column 1. At 12 years, the FW$1 factor is approximately equal to 2, indicating a doubling (the actual factor is 2.012196).

Image of a compound interest table (AH 505, page 33) highlighting the future worth of one dollar factor for 12 years with annual compounding at an annual interest rate of 6 percent. The highlighted factor is 2.012196.

Link to AH 505, page 33



Example 2:
Eight years ago you received a small inheritance that you deposited in a savings account. The amount has now doubled. What compound annual interest rate have you earned over the past 8 years?

Solution:
Image showing the formula for the Rule of 72. The annual interest rate is equal to 72 divided by the number of years to double, in this example, 72 divided by 8 years, which equals 9 percent.

To confirm the estimate, search in AH 505 for the annual rate at which the FW$1 factor for 8 years is approximately equal to 2, indicating a doubling. In AH 505, page 45, column 1, the FW$1 factor at 8 years is approximately equal to 2 (the actual factor is 1.992563).

Image of a compound interest table (AH 505, page 45) highlighting the future worth of one dollar factor for 8 years with annual compounding at an annual interest rate of 9 percent. The highlighted factor is 1.992563.

Link to AH 505, page 45



Example 3:
You’ve purchased a house that you think will double in value in 10 years. At what annual compound rate will the property have appreciated?

Solution:
Image showing the formula for the Rule of 72. The annual interest rate is equal to 72 divided by the number of years to double, in this example, 72 divided by 10 years, which equals 7.2 percent.

At an annual rate of 7.00% the FW$1 factor for 10 years is 1.967151 (AH 505, page 37).

Image of a compound interest table (AH 505, page 37) highlighting the future worth of one dollar factor for 10 years with annual compounding at an annual interest rate of 7 percent. The highlighted factor is 1.967151.

Link to AH 505, page 37


At an annual rate of 7.50% the FW$1 factor for 10 years is 2.061032 (AH 505, page 39).

Image of a compound interest table (AH 505, page 39) highlighting the future worth of one dollar factor for 10 years with annual compounding at an annual interest rate of 7.5 percent. The highlighted factor is 2.061032.

Link to AH 505, page 39

Interpolating, the annual rate at which the FW$1 factor is 2, is somewhere between 7.00 and 7.50%, approximately 7.2%.



Multiple Payments and FW$1

We have calculated the future value of single amounts or payments, using the FW$1 factor.

Many problems involve more than one payment, making it necessary to calculate the future value of multiple payments–that is, the future value of a stream of payments. Determining the future value of multiple payments is a straightforward extension of the single-payment situation.

When we calculated the future value of a single amount or payment, we multiplied the payment by the appropriate FW$1 factor. This compounded the payment to its future value.

If there is more than one payment, we must multiply each payment by the appropriate FW$1 factor and add up all of the future values. The sum of the future values is the total future value of the stream of payments.



Practical Applications of FW$1 with Multiple Payments

Example 1
You plan to make the following three deposits into a savings account:

  1. $10,000 at the end of the first year
  2. $15,000 at the end of the second year
  3. $20,000 at the end of the third year


At an annual interest rate of 5%, how much will you have in the account at the end of the third year (i.e., what is the total future value of all three payments)?

Solution:
Calculate the future value of each payment as of the end of year 3 using the appropriate FW$1 factor (AH 505, page 29, column 1) and add those future values. This sum is the future value of all three payments at the end of 3 years.

Thus:

Image of a table showing three payments multiplied by the appropriate FW$1 factors to arrive at future values, and then summing to arrive at the total future value of the three payments. 
A payment of $10,000 multiplied by 1.102500, the FW$1 factor for 2 years at an annual interest rate of 5 percent, given annual compounding. The resulting future value is equal to $11,025
A payment of $15,000 multiplied by 1.050000, the FW$1 factor for 1 year at an annual interest rate of 5 percent, given annual compounding. The resulting future value is equal to $15,750
A payment of $20,000 multiplied by a factor of 1.0, which reflects no compounding because the payment occurs at the end of year 3. The future value is equal to $20,000, same as the payment amount.
Adding the three values above, the table shows a total future value for the three payments at the end of year 3 of $46,775

The first payment is compounded forward for two periods (years); the second payment for one period (year); and the final payment, which itself at the end of year 3, requires no compounding.


Image of a compound interest table (AH 505, page 29) highlighting the future worth of one dollar factor for 1 and 2 years with annual compounding at an annual interest rate of 5 percent. The highlighted factors are 1.050000 for 1 year and 1.102500 for 2 years.

Link to AH 505, page 29


Viewed on a Timeline:

Image that depicts the calculations in the preceding table on a timeline, showing the future value for each of the three payments and the total future value of $46,775 as of the end of year 3.

On the timeline, the deposits are shown as negative because from the perspective of the depositor they represent cash outflows, and the resulting future values are shown as positive because they represent cash inflows at the end of year 3.