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Rule of 72

How long until this return doubles the money, and what is the exact compound time?

Your numbers

Years to double

9

Doubled value$20,000
Exact compound years at this rate9.01

Tip. Educational estimate with the assumptions listed on this page. Not tax, legal, or investment advice.

Assumptions

  • Return is constant and compounds annually.
  • Taxes, fees, and contributions are ignored.
  • The Rule of 72 is an approximation; the exact line is also shown.

Explore the numbers

Examples

Load a scenario, then change one input at a time.

Example 1

Index-like 8%

Default.

Years to double

9

Example 2

After fees 7%

Same capital, 1% fee.

Years to double

10.29

Example 3

High-yield 12%

Optimistic private deal rate.

Years to double

6

What this calculates

Estimate doubling time with the Rule of 72 and show the exact compound-interest years next to it.

How to use it

  1. Use a net-of-fee expected return, not a best year.
  2. Compare 6%, 8%, and 10% so you do not treat one rate as fate.
  3. If you add money monthly, use compound savings growth instead.

Common mistakes

  • Using a 20% year as if it repeats.
  • Ignoring fees, which are a direct cut to the rate.
  • Applying it to a leveraged deal with principal risk.

Formula

Rule of 72 years = 72 ÷ annual percent return. Exact years = ln(2) ÷ ln(1 + r).

FAQ

Why 72?

It is a mental-math approximation that stays close for common rates around 6% to 10%.

Does inflation change this?

Use a real return if you want doubling of purchasing power.

How do investment fees change doubling?

A 1% fee on an 8% return is a 7% return. Plug the net number.

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