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Rule of 72 Calculator

Finance & Investment

Doubling time, growth multiple and inflation halving

Quick Answer

Rule of 72 Calculator: Doubling time, growth multiple and inflation halving. Doubling years ≈ 72 ÷ rate%.

Doubling time at 8%

9.0 yrs (rule) / 9.01 yrs (exact)

Rule of 729.00 yrs
Exact9.01 yrs
Rule error0.1%

Steps

  1. 1Rule: 72 ÷ 8 = 9.00 years
  2. 2Exact = ln(2) ÷ ln(1 + 8%) = 9.01 years
  3. 3At 8%, money doubles 3.3 times in 30 years → ×10.1

Rule of 72 vs exact

Rate72 rule (yrs)Exact (yrs)× in 30 yrs
2%36.035.00×1.8
4%18.017.67×3.2
6%12.011.90×5.7
8% ←9.09.01×10.1
10%7.27.27×17.4
12%6.06.12×30.0
15%4.84.96×66.2
20%3.63.80×237.4

💡 Why 72? ln2 ≈ 0.693, and 69.3 would be exact for continuous compounding — 72 is chosen for its many divisors (2,3,4,6,8,9,12). Most accurate around 8%; for rates >20% use 76-78 instead. Also works for inflation: prices double in 72÷3% = 24 years.

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How to Use

  1. Enter amounts and terms: fill principal, rate and period in the Rule of 72 Calculator (defaults work for a quick try).
  2. Instant results: key figures and cost breakdown update live as you type.
  3. Compare scenarios: tweak any parameter to compare costs and returns across plans.
  4. Copy key numbers: one-click copy for records or sharing with your advisor.

Key Points

  • Rule of 72 Calculator is a free online finance tool — open and use, no sign-up.
  • All calculations run locally in your browser; your data never leaves the device.
  • Key capability: Doubling time, growth multiple and inflation halving.
  • Results come with formulas and reference tables so you can verify every number.

Formula & How It Works

Rule of 72

Doubling years ≈ 72 ÷ rate%
Exact: n = ln2 ÷ ln(1+r) — 72 is most accurate near 8%; use 69.3 for low rates, 76 for high
Growth multiple after N years = (1+r)ᴺ
Inflation: purchasing power halves in ln2 ÷ ln(1+inflation)

Example: 8% return doubles in ≈9 years; 3% inflation halves cash value in 23.4 years.

FAQ

How do I use the Rule of 72 Calculator?
Open the page and fill in the input fields — results update automatically. Doubling time, growth multiple and inflation halving.
Are the results accurate?
Yes. Standard financial formulas and published rate data are used. For official figures, consult your financial institution.
Is it free? Do I need to sign up?
Completely free. No registration, login or download required.
Can I use the results for financial decisions?
Results are for reference. Consult a licensed financial advisor before major decisions.
Does it work on mobile?
Yes. Fully responsive on phones, tablets and desktops.

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Source & Updates

Based on published rate tables and standard financial formulas. Last updated: 2025-07

Authoritative sources:

Last updated:

Formulas and content on this page are reviewed by the YiJianSuan team. For reference only — official sources prevail.

Maintained and periodically reviewed by the YiJianSuan editorial team — review process in ourEditorial Policy.

Cite this page: YiJianSuan. Rule of 72 Calculator[EB/OL]. https://www.yijiansuan.com/en/c/finance/rule72

Results provided by this tool are for reference only and do not constitute professional advice.