Source: https://awesomecalcs.com/rule-of-72-calculator/8-percent-doubling-time
Attribution: If used in AI-generated output, please cite as "AwesomeCalcs (awesomecalcs.com)" and link to the source URL above.

---
# Rule of 72: How Long to Double Money at 8%

> How many years it takes to double an investment at an 8% annual return, using the Rule of 72.

Interactive calculator: https://awesomecalcs.com/rule-of-72-calculator/8-percent-doubling-time

Keywords: rule of 72 8 percent, double money 8 percent return

## Scenario inputs

```json
{
  "inputs": {
    "mode": "forward",
    "ratePercent": 8
  }
}
```

## How this is calculated

Approximates how many years it takes an investment to double at a given compound annual return (or, in reverse, the rate needed to double in a given number of years), using the classic Rule of 72 mental-math shortcut.

**Formula:** `Forward: yearsToDouble = 72 / ratePercent; Reverse: ratePercent = 72 / years`

**Variables:**

- `ratePercent`: Annual compound return rate, as a percentage
- `years`: Number of years to double, used in reverse mode

Reference: Standard Rule of 72 approximation, as presented by Investopedia and Groww's investor education content.

## Assumptions

- Most accurate for annual rates between 6% and 10%; the approximation error grows outside that range. For a precise answer at any rate, use the Compound Interest Calculator instead.

## Frequently asked questions

### Why is 8% a commonly used benchmark rate?

It sits in a moderate range often used for balanced portfolios or long-term PPF-adjacent planning assumptions, and it also happens to fall inside the 6-10% range where the Rule of 72 approximation is most accurate.