Compound Interest Calculator
Estimate how your USD investment grows over time. We use a default 5% annual rate, but long-term stock returns average around 7% per year after inflation.
Typical long-term market return ≈7%.
Results
After 10 years, your balance could grow to $17,175.24. You contributed $13,000, earning $4,175.24 in interest.
What Is Compound Interest?
Compound interest is interest on interest. You earn on your initial principal *and* on previously earned interest. Over years, this accelerates growth dramatically— the longer you invest, the stronger the effect.
Why Use This Calculator?
Experiment with different rates and contributions:
- See how a higher rate (e.g., 7% vs. 5%) impacts final balance.
- Understand the power of consistent monthly investing.
- Plan your savings goals by adjusting duration and contributions.
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Mnemonic Rules for Compound Interest
- Rule #1: Your money doubles approximately every 10 years. After 20 years it’s about 4×, after 30 years roughly 8×.
- Rule #2: Save $100 per month for about 12 years to receive $100 per month for life (the same principle behind many FIRE calculators).
- Rule #3: Money doubles after approximately 72 ÷ interest rate (%) years. For example, at 10% annual return: 72 ÷ 10 = ~7.2 years.
- Rule #4: Money triples after roughly 115 ÷ interest rate (%) years. At 10%: 115 ÷ 10 = ~11.5 years.
- Rule #5:
- Eliminating a $1 monthly expense today can grow to ~$187 in 10 years at 8% return.
- Eliminating a $1 weekly expense today can grow to ~$750 in 10 years at 8% return.
These rules assume an 8% annual return (typical for a broad, passive index fund). Always consider inflation and taxes when planning.