Rule of 72 Calculator

💰 How This Calculator Works

Estimates the time required to double an investment using the quick formula: years = 72 ÷ annual rate (%).

🔢 Worked Examples

• 6% → doubles in 12 years
• 9% → doubles in 8 years
• 3% inflation → prices double in 24 years
• 1% savings rate → 72 years to double

📋 Common Use Cases

Interest calculators cover compound interest, simple interest, and time-value-of-money concepts. Understanding the difference between nominal and effective rates — and how compounding frequency affects returns — can mean thousands of dollars difference over a savings or investment horizon.

• Comparing savings account yields by compounding frequency
• Computing the true annual rate from a monthly-quoted rate
• Projecting investment growth under different return assumptions
• Understanding the "Rule of 72" for doubling time

💡 Did You Know?

Daily compounding at 5% annual grows money to 5.127% effective rate. Compounding matters more the longer you invest — the difference between annual and daily compounding on a 30-year $10,000 investment is over $1,500.

⚠️ Common Mistake

Using the rule beyond its accuracy range — it works best between 6–10%. Below 5% or above 15%, errors grow. For 1%, use Rule of 70; for 25%, use 72 ÷ 25 ≈ 2.9 but verify with the exact formula.