How does the rule of 72 work?

Divide 72 by the annual rate, written as a whole-number percent. The result is the approximate number of years for the amount to double at that rate, compounded once a year.

What are the rules of 114 and 144?

They are the same idea for other multiples. Divide 114 by the rate to estimate the years to triple, and 144 by the rate to estimate the years to quadruple.

How accurate is the rule of 72?

It is a close approximation, most accurate for rates around 6% to 10%. For an exact figure, use the logarithmic formula or a compound-interest calculator.

Does it work for inflation?

Yes. Divide 72 by the inflation rate to estimate how many years it takes for prices to double, or for purchasing power to halve.

Should I enter the rate as a percent or a decimal?

Enter it as a percent. For 8%, type 8, not 0.08. The rule divides 72 by that percent figure directly.

Can I share a calculation?

Yes. Use Share to copy a link that reopens the calculator with the same rate.

Rule of 72 calculator

Enter an annual growth or interest rate. The calculator shows the approximate number of years to double (rule of 72), triple (rule of 114), and quadruple (rule of 144) as you type.

Divide 72 by the annual rate to estimate the years to double. The rule of 114 estimates tripling and the rule of 144 estimates quadrupling.

Years to double

9 yr

Years to triple: 14.3 yr
Years to quadruple: 18 yr

The result updates as you type. Years to double is the headline figure; tripling and quadrupling are shown below as quick approximations.

How does it work?

These are quick approximations, not exact figures. They are most accurate for rates around 6–10% and assume a single constant rate. You supply the rate yourself; the calculator does not look one up.

Rule of 72 formula

t \approx \frac{72}{r}

t: Approximate years for the balance to double.
r: Annual growth or interest rate, in percent.

At 8% the balance doubles in about 9 years (72 ÷ 8). The rule of 114 estimates tripling (about 14.25 years) and the rule of 144 estimates quadrupling (about 18 years).

Method & sources

The rule of 72 is an approximation, not an exact formula; the precise doubling time comes from logarithms. It is most accurate for rates roughly between 6% and 10%; far outside that range the estimate drifts. It assumes a single constant compounding rate over the whole period.

Sources

Where this method comes from — use these references to understand the formula, assumptions, and limits.

Rule of 72 — compound interest shortcut — U.S. Securities and Exchange Commission (Investor.gov), verified 2026-06-10

How we calculate

The rule of 72 is an approximation, not an exact formula; the precise doubling time comes from logarithms.
It is most accurate for rates roughly between 6% and 10%; far outside that range the estimate drifts.
It assumes a single constant compounding rate over the whole period.
You supply the rate yourself; the calculator does not look up market rates.
Fees, taxes, and additional contributions are not included.

Rounding

Years are rounded to one decimal for display. The calculation uses full precision.

What this calculator does

The rule of 72 is a mental-math shortcut for compound growth. Divide 72 by the annual rate (as a whole-number percent) and you get the approximate number of years for a balance to double. This calculator does that division for you, then applies the related rules of 114 and 144 to estimate tripling and quadrupling.

How to use it

Enter the annual growth or interest rate as a percentage.
Read the approximate years to double below.
Check the years to triple and quadruple for the same rate.

A worked example

At an 8% annual rate, 72 ÷ 8 = 9, so a balance doubles in about 9 years. The rule of 114 gives 114 ÷ 8 ≈ 14.25 years to triple, and the rule of 144 gives 144 ÷ 8 = 18 years to quadruple.

Why 72?

The exact doubling time comes from logarithms, but 72 is easy to divide and lands close to the real answer for typical rates. It is most accurate between about 6% and 10%; outside that range the estimate drifts a little.

Common mistakes

Entering the rate as a decimal (0.08) instead of a percent (8).
Treating the result as exact. It is a quick approximation, not a precise figure.
Mixing in fees, taxes, or contributions. The rule works on the rate alone.

When it's useful

Sizing up investment returns, savings rates, or even inflation in your head, or sanity-checking a longer compound-interest projection.

FAQ

How does the rule of 72 work?: Divide 72 by the annual rate, written as a whole-number percent. The result is the approximate number of years for the amount to double at that rate, compounded once a year.
What are the rules of 114 and 144?: They are the same idea for other multiples. Divide 114 by the rate to estimate the years to triple, and 144 by the rate to estimate the years to quadruple.
How accurate is the rule of 72?: It is a close approximation, most accurate for rates around 6% to 10%. For an exact figure, use the logarithmic formula or a compound-interest calculator.
Does it work for inflation?: Yes. Divide 72 by the inflation rate to estimate how many years it takes for prices to double, or for purchasing power to halve.
Should I enter the rate as a percent or a decimal?: Enter it as a percent. For 8%, type 8, not 0.08. The rule divides 72 by that percent figure directly.
Can I share a calculation?: Yes. Use Share to copy a link that reopens the calculator with the same rate.

Related calculators

Embed this calculator

Add this calculator to your own site. The snippet includes the calculator iframe and a small attribution link:

<iframe src="https://wisecalcs.com/embed/en/rule-of-72-calculator" width="100%" height="520" style="border:0" loading="lazy"></iframe>
<p>Calculator from <a href="https://wisecalcs.com/en/investments-retirement/rule-of-72-calculator">WiseCalcs</a></p>