Thursday, March 13, 2008

Power of Compounding (Rule of 72 & Rule of 70)

In finance, these rules are methods to estimate the time of an investment’s doubling (exponential growth) or halving (decay).

Let’s try, you use initial capital with $1,000 and increase the value by 20% annually see how many year it takes to double the initial value.

Year 1: $1,000 × 20% = $200
Year 2: ($1,000 + $200) × 20% = $240
Year 3: ($1,200 + $240) × 20% = $288
Year 4: ($1,440 + $288) × 20% = $345.60

End of year 4, the value has double from $1,000 to $2073.60. This means it takes between 3 to 4 years to double the value by 20% increment.

Rule of 72:
This is to estimate the number of periods required to double an original investment, divide the most convenient "rule-quantity" by the expected growth rate, expressed as a percentage.

72 ÷ (Annual Percentage return) = number of years your investment would double

For instance, if you were to invest $1,000 with compounding interest at a rate of 20% per annum, the rule of 72 gives 72 ÷ 20 = 3.6 years required for the investment to be worth $2,000.

Rule of 70:
Similarly, to determine the time it takes for the value of money to half at a given rate, divide the rule quantity by that rate.

70 ÷ (Rate) = Time period of the value become half

Example, if the inflation rate is 3.5%, the value of the money we have will be half in 20 years. Use the rule of 70, 70 ÷ 3.5 = 20. It can be use to estimate the impact of the additional fees on financial policies such as unit trust, mutual fund, load, insurance, expenses etc.

No comments: