# Rule of 72 Calculator

URL: https://speedycalculator.com/calculators/finance/rule-of-72/
Last updated: 2026-10-25

> The rule of 72 calculator estimates how long it takes an investment to double at a given annual rate – 72 divided by the rate – and compares it with the exact answer, the rule of 70 and the rule of 69.3, or works out the rate needed to double in a given time.

## Inputs

- Annual rate of return (%)
- Or: years in which to double

## Results

- Years to double (rule of 72)
- Exact years to double
- Rule of 70
- Rule of 69.3 (continuous)
- Rate needed to double in your years (rule of 72)
- Exact rate to double

## Formula

```
Years to double ≈ 72 ÷ rate (%)
Exact: years = ln 2 ÷ ln(1 + r)
Rule of 69.3 is exact for continuous compounding
Rate to double in t years ≈ 72 ÷ t; exact: 2^(1/t) − 1
```

## Explanation

The rule of 72 works best for rates of about 6–10%. It also works for anything growing exponentially – like inflation: at 3% inflation prices double in about 24 years.

### How to use the Rule of 72 Calculator

- **Annual rate of return**
- **Or: years in which to double**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the annual rate of return (or growth) and, optionally, a target number of years to double.

### Tips

- Start early – time does more of the work than the amount you save.
- Take the full employer match if your plan offers one.
- Plan with a cautious return (4–6% after inflation) and check again every year.
- Know the contribution limits and required minimum distribution rules for your accounts.

### Common mistakes to avoid

- Ignoring inflation when setting a retirement target.
- Underestimating how long retirement can last.
- Withdrawing early and paying penalties and taxes.

### Inputs explained

FieldWhat to enterAnnual rate of returnIn %Or: years in which to doubleA number

### What each result means

- **Years to double (rule of 72)** = 72÷[Annual rate of return]
- **Exact years to double** = log(2)÷log(1 + [Annual rate of return]÷100)
- **Rule of 70** = 70÷[Annual rate of return]
- **Rule of 69.3 (continuous)** = 69.3÷[Annual rate of return]
- **Rate needed to double in your years (rule of 72)** = 72÷[Or: years in which to double]
- **Exact rate to double** = (2^(1÷[Or: years in which to double]) - 1)×100

### Example values

How the main result changes when **Annual rate of return** changes and everything else stays at the example values above:

Annual rate of return (%)Years to double (rule of 72)41861289107.2126164.5

## Worked example

Inputs — Annual rate of return: 8 %; Or: years in which to double: 10.

Results — **Years to double (rule of 72) = 9**; Exact years to double = 9.01; Rule of 70 = 8.75; Rule of 69.3 (continuous) = 8.66; Rate needed to double in your years (rule of 72) = 7.2 %; Exact rate to double = 7.177 %.

## FAQ

**What is the rule of 72?**
A shortcut: 72 ÷ the annual rate ≈ years for money to double.

**How accurate is it?**
Within a few months for rates of 4–12%.

**Can I use it for inflation?**
Yes – 72 ÷ inflation rate is how long until prices double.

**What formula does the Rule of 72 Calculator use?**
Years to double ≈ 72 ÷ rate (%).


## Sources

- [U.S. SEC – Investor.gov compound interest and investing basics](https://www.investor.gov/)