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 Break Even Point
 Payback Period & Discounted Payback Period
 Payback period Formula
 Discounted Payback Period Formula
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 Loan Amortization Schedule
 Rule of 72
 Geometric Mean Return
 Real Rate of Return Formula
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 Holding Period Return Formula
 Cost Benefit Analysis
 Mortgage APR vs Interest Rate
Rule of 72 Formula
In simple terms, Rule of 72 is a formula that helps us understand when we can double our investment.
Here’s how it works.
As an investor, you need to know the rate of return. And then all you need to do is to take the number 72 and divide it by the rate of return. And you will get the duration of time that will double your investment.
Here’s the formula –
Here, r = the rate of return
Alternatively, there can be another 72 rule formula.
In that formula, you would be able to know the rate of return at which you would be able to double your investment.
Here’s the alternative formula –
Here. t = duration of time
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Example of Rule of 72 Formulas
Let’s take a simple example to illustrate 72 rule formulas.
Deeds Inc. has been offering 9% return on the investment of $200,000. Find out when the money will get double. Also if the investors want to double their money in 6 years, what would be the available rate?
By using the first formula of 72 rule, we get –
 72 rule = 72 / r = 72 / 9 = 8 years.
 It will take 8 years to double the money.
Coming to the next question, we can use the second formula of Rule of 72.
 72 rule = 72 / t = 72 / 6 = 12%.
 At 12% rate, the investors can double the money within 6 years.
Explanation of Rule of 72 Formulas
Let’s understand the above two formulas in detail.
The first formula is all about “when”.
And the next formula is all about “what rate”.
 In the first formula, the investor isn’t sure about the time duration of the investment. She needs to use the formula to come to a conclusion.
 In the second formula, the investor isn’t sure about the rate of return on the investment. In other words, in the second formula, the investor isn’t sure at what rate she would be able to double her investment.
As an investor, you should use both.
 Let’s say that you’re investing a sum of $100,000 into an investment. They are offering you a 10% return.
 Using the first formula of 72 rule, we can easily find out when you will double your investment.
 72 Rule = 72 / r = 72 / 10 = 7.2 years.
 Now, let’s say that the investor wants the money to double within 6 years.
What should she do in that case?
 She needs to use the second formula of 72 rule to reach the conclusion.
 Rule of 72 = 72 / t = 72 / 6 = 12%.
 To double the money the investor puts into the investment within 6 years, she needs to get a rate of return of 12%.
Use of Rule of 72 Formulas
 If an investor needs to know the basics about the investments, she should have formulas that are useful and at the same time can deliver quick results. 72 rule formulas are very useful and can help the investors quickly.
 Even if the investors don’t know anything about investment, they can quickly use these formulas to know the basics of the investments. However, 72 rule formulas can’t act as substitutes of financial ratios.
 You can use 72 rule formulas quickly to find out the rate or the time period when your investment will get doubled. But, keep in mind, 72 rule formulas alone aren’t enough. You need to look at all the financial statements and also investigate all the financial ratios of the company before investing.
Rule of 72 Formulas Calculator
You can use the following Rule of 72 formula Calculator.
Rate of Return (r)  
Rule of 72 Formula =  
Rule of 72 Formula = 


Rule of 72 Formulas in Excel (with excel template)
Let us now do the same example above in Excel.
This is very simple. You can easily calculate the ratio in the template provided.
You can download this Rule of 72 formula here –Rule of 72 formula Excel Template
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