Which statement best describes the effect of inflation on doubling time using the Rule of 72?

Which statement best describes the effect of inflation on doubling time using the Rule of 72?

• A. Inflation affects the doubling time; for example, at 6% inflation, it would take about 12 years for prices to double.
• B. Inflation has no impact on the Rule of 72.
• C. The Rule of 72 only applies to taxes.
• D. Double time is always the same regardless of rate.

Answer: (A)

The growth rate you’re using with the Rule of 72 is what determines how long it takes for something to double. If prices rise at a steady inflation rate, the doubling time is roughly 72 divided by that rate (as a percent). So with inflation at 6% per year, prices double in about 72/6 = 12 years. The exact calculation using the exponential model gives t ≈ ln(2)/ln(1.06) ≈ 11.6 years, which is close to 12, illustrating why the rule is a handy shortcut. This shows that inflation does affect doubling time: higher inflation shaves years off the time to double, while lower inflation extends it. The Rule of 72 isn’t limited to taxes and is not a constant regardless of rate; doubling time clearly depends on the rate.

The growth rate you’re using with the Rule of 72 is what determines how long it takes for something to double. If prices rise at a steady inflation rate, the doubling time is roughly 72 divided by that rate (as a percent). So with inflation at 6% per year, prices double in about 72/6 = 12 years. The exact calculation using the exponential model gives t ≈ ln(2)/ln(1.06) ≈ 11.6 years, which is close to 12, illustrating why the rule is a handy shortcut. This shows that inflation does affect doubling time: higher inflation shaves years off the time to double, while lower inflation extends it. The Rule of 72 isn’t limited to taxes and is not a constant regardless of rate; doubling time clearly depends on the rate.