Time to Double Money Calculator

💰 How This Calculator Works

Calculates the exact doubling time for an investment at a given interest rate.

🔢 Worked Examples

• 5%: exact 14.21yr, Rule of 72 → 14.4yr
• 10%: exact 7.27yr, Rule of 72 → 7.2yr
• 2%: exact 35.0yr, Rule of 72 → 36yr

📋 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

The Rule of 72 becomes inaccurate at extreme rates. At 1%, it says 72yr but the exact answer is 69.66yr. At 50%, it says 1.44yr but the exact answer is 1.71yr.