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Rule of 72 Calculator

Calculate investment doubling timelines, target rate requirements, and inflation purchasing power loss.

Disclaimer: All calculations and figures are provided for informational purposes only and without warranty. This does not constitute legal, tax, or financial advice. Liability for any decisions made based on this calculator is disclaimed.
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2. Capital & Rate Inputs

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💡 Die 72er-Regel: Teilen Sie 72 durch den Zinssatz, um die Jahre bis zur Verdopplung zu ermitteln (72 / 7 % = 10.3 Jahre).

Time to Double Investment
10.3 Years

Exact compound formula: 10.2 years (variance: only ~0.5 months).

Portfolio after 1st Doubling
$40,000.00

Based on an initial capital of $20,000.00.

📈 Compound Growth Multipliers

1. Cycle (10.3 yrs) $40,000.002x Startkapital
2. Cycle (20.6 yrs) $80,000.004x Startkapital
3. Cycle (30.9 yrs) $160,000.008x Startkapital
4. Cycle (41.1 yrs) $320,000.0016x Startkapital

The Rule of 72: Mastering Exponential Compounding Mental Math

The Rule of 72 is the most intuitive mental model in finance, transforming complex logarithmic compounding into simple division.

1. Core Equations

  • Years to Double: 72 / Annual Interest Rate (%)
  • Required Rate of Return: 72 / Target Years
  • Inflation Half-Life: 72 / Annual Inflation Rate (%)
  • Exact Formula: ln(2) / ln(1 + r)

2. Portfolio Doubling Horizons

At 3% fixed yield, capital doubles every 24 years. At 7% equity index return, it doubles every 10.3 years. At 10% growth, wealth doubles every 7.2 years ($10k turns into $80k after three cycles / ~21.6 years).

Frequently Asked Questions (FAQ)

What is the Rule of 72 and how does it work?▼

The Rule of 72 is a financial shortcut used to estimate the number of years required to double invested capital at a fixed annual rate of return. Simply divide 72 by the annual return percentage: Years to Double = 72 / Rate of Return.

How accurate is the Rule of 72 compared to the exact compound interest formula?▼

For typical investment returns between 4% and 12%, the Rule of 72 is remarkably accurate. At a 7% return, the Rule of 72 predicts 10.29 years, while the exact formula (ln(2) / ln(1.07)) yields 10.24 years—a difference of under a single month.

How does the Rule of 72 apply to inflation and purchasing power?▼

By dividing 72 by the annual inflation rate, you calculate the purchasing power half-life: how many years it takes for cash to lose half of its real buying power (e.g. at 3% inflation: 72 / 3 = 24 years).

How do you calculate the required rate of return for a target doubling horizon?▼

If you want to double your portfolio over a specific timeframe (e.g. 8 years), divide 72 by the target years: Required Annual Return = 72 / 8 = 9.0% p.a.

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