Compound Interest Calculator
Harness the power of "interest on interest" to build long-term wealth.
Optional Contributions
Compound Interest Calculator
Compound interest is the reason small, consistent savings become life-changing wealth. This calculator shows you exactly how fast your money grows when interest earns interest — with a year-by-year breakdown so you can see the snowball in action.
What Is Compound Interest?
Compound interest is interest calculated on both the principal and the accumulated interest from previous periods. Unlike simple interest (only on principal), compound interest grows exponentially — your earnings earn earnings.
How to Use This Calculator
- Enter your initial deposit (starting amount).
- Enter the annual interest rate.
- Select the compounding frequency: daily, monthly, quarterly, or annually.
- Enter the time period in years.
- Optionally add regular contributions (monthly or annually).
- Click Calculate to see your final balance and year-by-year growth table.
Compound Interest Formula
A = P × (1 + r/n)^(n × t)
- A = Final amount | P = Principal | r = Annual rate (decimal) | n = Compounding periods/year | t = Years
Example: Power of Compounding
Principal: $10,000 | Rate: 8% | Compounding: monthly
- After 10 years: $22,196
- After 20 years: $49,268
- After 30 years: $109,357
Without compounding (simple interest): $10,000 + $24,000 interest = $34,000 after 30 years. Compounding delivers $75,357 more.
Compounding Frequency Comparison ($10,000 at 8% for 30 years)
- Annually: $100,627
- Quarterly: $107,652
- Monthly: $109,357
- Daily: $110,232
Common Mistakes to Avoid
- Withdrawing interest earnings — Taking out earnings stops the compounding effect. Let it reinvest and grow.
- Underestimating inflation — 8% nominal return is about 5% real return. Plan for inflation-adjusted goals.
- Comparing simple to compound rates — Savings accounts advertise APY (which includes compounding). APY is always higher than APR.
- Starting late — Starting 10 years earlier often leads to a dramatically larger final balance than doubling contributions.
Frequently Asked Questions
What is the Rule of 72?
Divide 72 by the annual interest rate to estimate how many years it takes to double your money. At 8%: 72 ÷ 8 = 9 years to double. At 6%: 12 years.
How does daily compounding differ from monthly?
Daily compounding earns slightly more because interest is recalculated and added each day. The difference is small — usually less than 1% total — but it compounds over decades.
Does compound interest work on debt too?
Yes — and it's devastating. Credit card debt at 24% compounding daily grows extremely fast. See our Credit Card Calculator to see how quickly debt can spiral.
What investment returns realistic compound interest?
Broad stock market index funds (S&P 500) have historically returned ~10% nominal, ~7% inflation-adjusted. High-yield savings accounts currently offer 4%–5%. Use both scenarios to bracket your expectations.
Can I calculate compound interest with regular contributions?
Yes — our calculator includes this. Adding regular contributions dramatically accelerates growth. See our Investment Calculator for a detailed contribution model.
Conclusion
The math of compound interest rewards patience above everything. The best time to start investing was yesterday. The second-best time is today. Use this calculator to see exactly what starting now — versus waiting five more years — costs you in final wealth.
Related: Simple Interest Calculator | Investment Calculator | Savings Calculator | Interest Rate Calculator
Financial Tip
Don't wait! Starting just 5 years earlier can result in a 50% larger final balance due to the compounding effect in the final years of your investment.
