Rule of 72

The Rule of 72 is a calculation that evaluates the number of years it takes to double your cash at a nominal rate of return.

If, as an example

Your account earns 8% per year.

That 72 divided by 8 to get the number of years it'll hold your cash to double.

72 / 8 = 9 year 

What is the rule of 72 in math?

Rule of  72 in mathematics, is an easy way to confirm how long to calculate investment can go for double given a fixed annual rate of interest. By dividing 72 by the annual rate of return, investors get a rough estimate of what percentage years it'll hold the initial investment to duplicate itself.

What is the Rule 72?

In finance, the Rule of 72 is a formula that estimates the amount of your time it takes for an investment to double in value, earning a fixed annual rate of return. Rule of  72 on the other side of the coin, is the calculation to see the amount of time for an investment to double in price. the easy calculation is dividing seventy-two by the annual rate.

Rule of 72 Formula for Simple Interest

  • Doubling time (Number of years ) = 72 / Annual rate

Example of Rule 72

If you're the owner of a Chocolate manufacturing company. because of the massive capital required to determine a manufacturing plant and warehouse for chocolate-creating machines, you have got turned to personal investors to fund the expenditure. You meet with Jhon, who could be a high net-worth individual willing to contribute RS10,00,000 to your company.

However, Jhon is simply willing to contribute the same quantity on the presumption that he will get a 12% annual rate of return on his investment, combined yearly. He desires to grasp however long it'll hold his investment in your company to double in price.

Rule of 72 Formula for Simple Interest

Doubling time (Number of years ) = 72 /12 = 6 years

It will take just about 6 years for Jhon's investment to get double in price

How to use Rule 72 to double investor investment?

Time (Years) to Double Investment

  • The Rule of 72 offers an estimation of the doubling time for an investment. it's a reasonably correct activity and a lot of this once uses lower interest rates instead of higher ones. it's used for things involving compound interest. a simple interest rate doesn't work well with Rule of 72.

Rule of 72 Formula for Compound Interest

  • The formula for Rule 72
  • Rule 72 will be expressed merely as:
  • Years to double = 72 / rate of come on investment (or interest rate)
  • There are a couple of vital conditions to know with the formula:
  • The rate shouldn’t be expressed as a decimal out of one, such as 0.07 for 7 p.c. It ought to simply be the number seven. So, as an example, 72/7 is 10.3, or 10.3 years.
  • Rule 72 is concentrated on compounding interest that compounds annually.
  • For simple interest, you’d merely divide one by the rate of interest expressed as a decimal. If you had $100 with a 10% p.c interest rate with no combination, you’d divide one by 0.1, yielding a doubling rate of ten years.
  • For continuous compounding interest, you’ll get a lot of correct results by using 69.3 rather than 72. The Rule of 72 is an estimate, and 69.3 is tougher for mental scientific discipline than 72, that divides simply by 2, 3, 4, 6, 8, 9, and 12. If you have got a calculator, however, use 69.3 for slightly a lot of correct results.
  • The farther you diverge from an 8 % come, the less correct your results are. The Rule of 72 works best within the vary of 5 to 12, however, it’s still an approximation.
  • To calculate support a lower rate, like 2 %, drop the 72 to 71; to calculate supported a better rate, add one to 72 for each 3 percentage point increase. So, as an example, use 74 if you’re calculating doubling time for 18% interest.

How does the Rule of 72 work?

  • The actual mathematical formula is advanced and derives the number of years till doubling supported the value of cash.
  • You’d begin with the long-run price calculation for periodic combination rates of come, a calculation that helps anyone curious about calculating exponential growth or decay:

FV = PV * (1+r) t

  • FV is future price, PV is present price, r is the rate and therefore the t is the period. To exclude t once it’s placed in an exponent, you'll take the natural logarithms of either side.
  • Natural logarithms are a mathematical way to solve for a disciple. A log of a number is the number’s logarithm to the power of e, an irrational mathematical constant that's roughly 2.718. With the example of a doubling of $10, the derivation of the Rule of 72 would seem like this:
  1. 20 = 10*(1+r)t
  2. 20/10 = 10*(1+r)t/10
  3. 2 = (1+r)t
  4. ln(2) = ln((1+r)t)
  5. ln(2) = r*t
  • The natural log of 2 is 0.693147, thus once you solve for t using those natural logarithms, you get t = 0.693147/r.
  • The actual results aren’t round numbers and are nearer to 69.3, however, 72 simply divides several of the common rates of coming that individuals get on their investments, thus rule 72 has gained popularity as a price to estimate doubling time.
  • For a lot of precise knowledge on how your investments are doubtless to grow, use a compound interest calculator that’s supported the total formula.

How to make use of the Rule of 72 for one's investment planning?

  • Most families' goal is to go on investment over time, typically monthly. You'll project however long it takes to urge to a given target amount if you've got an average rate of return and a current balance.
  • If, for instance, you've got RS 100,000, furnish nowadays at 10 % interest, and you're twenty-two years far away from retirement, you'll expect your cash to double some 3 times, going from RS 100,000 to RS 200,000, then to RS 400,000, and so to Rs800,000.
  • If your rate of interest changes otherwise you want extra money attributable to inflation or alternative factors, use the results from the Rule of72 to assist you to choose the way to keep investment over time.
  • You can conjointly use the Rule of 72 to form decisions regarding risk versus reward. If, for instance, you've got a low-risk investment that yields 2 % interest, you'll compare the doubling rate of thirty-six years there to of a speculative investment that yields 10 % and doubles in seven years.
  • Many young adults who are beginning out opt for risky investments as a result they need the chance to require advantage of high rates of coming for multiple doubling cycles. Those nearing retirement, however, can seemingly choose to invest in lower-risk accounts as they close to their target amount for retirement as a result doubling is a smaller amount necessary than investment in additional secure investments.


The Rule of 72 is a crucial guideline to stay in mind once considering what proportion to take a position. investment even a tiny low amount will build an enormous impact

if you begin early, and also the result will solely increase a lot of your investment because the power of combining works its magic. you'll conjointly use the Rule of 72 to assess however quickly you'll lose getting power in periods of inflation.


What's the reason for using the Rule of 72 calculators?

In finance, the Rule of 72 may be a formula that estimates the number of your time it takes for an investment to double in price, earning a set annual rate of return. The rule may be a cutoff, or back-of-the-envelope, the calculation to see the number of your time for an investment to double in price.