Rule of 72 Calculator

Estimate how many years it takes money to double based on annual return assumptions.

This calculator is part of the returns calculators hub cluster and supports scenario-based planning across adjacent entities.

Rule of 72 estimate

9 years

Exact doubling estimate

9.01 years

Insights

Generate a concise interpretation of your inputs and outputs. This is educational and hypothetical.

When This Calculator Can Mislead

Results can be misleading when assumptions are overly optimistic or inputs are inconsistent with real cash flow constraints.

Always test conservative and base-case assumptions and compare against related tools for contextual validation.

Contextual Links

What It Is

The Rule of 72 calculator estimates how long it takes an investment to double at a given annual return.

It also compares the quick estimate to an exact compounding-based doubling time.

How It Works

Rule of 72 estimate is computed as 72 divided by annual return percentage.

Exact doubling time uses logarithms with annual compounding assumptions.

Formula

Rule of 72 years = 72 / annual return (%).

Exact years = ln(2) / ln(1 + annual return as decimal).

Example

At 8% expected return, Rule of 72 gives about 9 years to double.

Use this as a fast heuristic, then validate with full projection tools for long-term planning.

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Frequently Asked Questions

Is Rule of 72 always accurate?

It is an approximation and is most accurate around mid-single to low-double-digit return rates.

What if returns vary every year?

The rule assumes a steady rate, so variable returns require scenario modeling with a detailed calculator.

Can I use it for inflation?

Yes. You can estimate how quickly prices double using an inflation rate input.

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