# Rule of 72 Calculator: Time or Rate Needed to Double an Investment This Rule of 72 Calculator will calculate the interest rate or the number of years needed to double your investment.

Plus, the calculator also includes options for other doubling rules (Rule of 69 and Rule of 70), as well as rules for tripling (Rule of 115) and quadrupling (Rule of 144).

Finally, the calculated results will include the formulas used to calculate the estimated and exact results, and, if you entered a starting amount, the investment's annual growth chart.

## Rule of 72 Calculator

Calculate the time or the interest rate needed to double your investment.

Special Instructions

#### Selected Data Record:

A Data Record is a set of calculator entries that are stored in your web browser's Local Storage. If a Data Record is currently selected in the "Data" tab, this line will list the name you gave to that data record. If no data record is selected, or you have no entries stored for this calculator, the line will display "None".

DataData recordData recordSelected data record: None
Rule:Rule:Multiple and rule:Multiple and rule:

#### Multiple and rule:

Select the rule and multiplier you would like the calculator to calculate for you, which will change the text in the result lines to reflect your selection.

Solve for:Solve for:Solve for:Solve for:

#### Solve for:

Select Number of Years to calculate the number of years it will take to double, triple, or quadruple your investment at the entered interest rate.

Select Interest Rate to calculate the annual interest rate you will need to earn to double, triple, or quadruple your investment within the entered number of years.

Rate:Rate:Annual interest rate:Annual interest rate:

#### Annual interest rate:

Enter the annual interest rate of the investment to see how long it will take to double, triple, or quadruple your investment at that rate.

 Annual interest rate %
Amount:Optional amt:Optional investment amount:Optional starting investment amount:

#### Optional starting investment amount:

If you would like to have an annual growth rate chart included in the results, enter the starting investment amount in this field. Otherwise, you can leave this field blank.

 \$ Optional starting investment amount
Rule 72 yrsRule 72 yearsRule of 72 yearsRule of 72 number of years:

#### Estimate:

If Interest Rate is selected:

Based on the selected rule and the entered annual interest rate, this is the estimated number of years it will take to double, triple, or quadruple your investment. The calculator will include a step-by-step completion of the formula used to calculate the estimated years.

If Number of Years is selected:

Based on the selected rule and the entered number of years, this is the estimated annual interest rate it will take to double, triple, or quadruple your investment. The calculator will include a step-by-step completion of the formula used to calculate the estimated interest rate.

Exact yrsExact yearsExact number of yearsExact number of years:

#### Exact:

If Interest Rate is selected:

Based on the selected rule and the entered annual interest rate, this is the exact number of years it will take to double, triple, or quadruple your investment. The calculator will include a step-by-step completion of the formula used to calculate the exact years.

If Number of Years is selected:

Based on the selected rule and the entered number of years, this is the exact annual interest rate it will take to double, triple, or quadruple your investment. The calculator will include a step-by-step completion of the formula used to calculate the exact interest rate.

If you would like to save the current entries to the secure online database, tap or click on the Data tab, select "New Data Record", give the data record a name, then tap or click the Save button. To save changes to previously saved entries, simply tap the Save button. Please select and "Clear" any data records you no longer need.

## Learn

### What the Rule of 72 is and how it is calculated.

#### What is the Rule of 72?

The Rule of 72 is a formula often used to quickly estimate the time or interest rate needed to double an investment having annual compounding growth.

Since the formula used to calculate the exact time or interest rate involves natural logarithms, and therefore usually requires a calculator or spreadsheet function to solve, the Rule of 72 gives a close approximation with simple math that can be performed in your head.

It's important to note that the closer the interest rate is to 8%, the closer the estimated doubling time will be to the exact doubling time.

#### How to Calculate Rule of 72

To calculate the number of years needed to double your investment, you would use the Rule of 72 formula shown as follows:

 Number or Years = 72 Interest Rate

For example, if your investment is earning 8% annually and you want to know how many years it will take double, you would plug the number 8 into the above formula.

 Number of Years = 72 8 Number of Years = 9

To calculate the interest rate needed to double your investment within a given number of years, you would use the Rule of 72 formula shown as follows:

 Interest Rate = 72 Number of Years

For example, if you want to know what annual interest rate will cause your money to double in four years, you would plug the number four into the preceding formula.

 Interest Rate = 72 4 Interest Rate = 18%

#### Rule of 72 Chart

The following chart shows how close the Rule of 72 formula comes to matching the exact number of years.

Interest RateEstimated Years to DoubleExact Years to Double
1%7269.66
2%3635
3%2423.45
4%1817.67
5%14.414.21
6%1211.9
7%10.2910.24
8%99.01
9%88.04
10%7.27.27
11%6.556.64
12%66.12
13%5.545.67
14%5.145.29
15%4.84.96
16%4.54.67
17%4.244.41
18%44.19
19%3.793.98
20%3.63.8

Move the slider to left and right to adjust the calculator width. Note that the Help and Tools panel will be hidden when the calculator is too wide to fit both on the screen. Moving the slider to the left will bring the instructions and tools panel back into view.

Also note that some calculators will reformat to accommodate the screen size as you make the calculator wider or narrower. If the calculator is narrow, columns of entry rows will be converted to a vertical entry form, whereas a wider calculator will display columns of entry rows, and the entry fields will be smaller in size ... since they will not need to be "thumb friendly".