Calculating your required growth rate is straightforward once you know the Doubling Rate Calculator (Rule of 72) formula and what each input means. This guide explains the method in plain language, walks through a manual calculation, and gives worked examples you can follow — then you can do it instantly with the Doubling Rate Calculator (Rule of 72).
What is Doubling Rate Calculator (Rule of 72)?
The Doubling Rate Calculator (Rule of 72) calculation tells you your required growth rate from a few simple inputs. The figure you are solving for here is the required growth rate, expressed in percent.
The Doubling Rate Calculator (Rule of 72) formula
The core formula is:
Required growth rate = 72 ÷ Years to doubleHere is what each input means:
- Years to double — a number. Example: 8.
How to calculate it step by step
- Write down the years to double (for example, 8).
- Apply the formula above to get your required growth rate.
- Double-check the result with the Doubling Rate Calculator (Rule of 72).
Worked examples
Example 1
| Input / Output | Value |
|---|---|
| Years to double | 8 |
| Required growth rate | 9.00% |
With years to double of 8, the required growth rate works out to 9.00%.
Example 2
With years to double of 16, the required growth rate works out to 4.50%.
| Result | Value |
|---|---|
| Required growth rate | 4.50% |
Example 3
With years to double of 4, the required growth rate works out to 18.00%.
| Result | Value |
|---|---|
| Required growth rate | 18.00% |
Tips for an accurate result
- Keep your units consistent — mixing, say, months with years or grams with kilograms is the most common source of error.
- Round only at the very end. Rounding inputs early can shift the final answer noticeably.
- Re-run the numbers whenever an input changes, rather than estimating from an old result.
- Annual rates must be converted to the period you are calculating for (for example, divide an annual rate by 12 for a monthly figure).
Prefer not to do the maths by hand? — the Doubling Rate Calculator (Rule of 72) does it instantly, for free, with the formula and a worked example built in.
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