Compound Interest Calculator
See how your savings or investments grow over time. Enter a starting amount, interest rate and time period, add regular monthly deposits, and compare compounding frequencies.
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How to use Compound Interest Calculator
- 1Enter your starting amount and the yearly interest rate.
- 2Choose how many years and how often interest compounds.
- 3Optionally add a monthly contribution.
- 4Read the final balance, total interest and the year-by-year breakdown.
Features
- Yearly, quarterly, monthly or daily compounding
- Optional monthly contributions
- Year-by-year balance table
- Total deposits vs. total interest
- Any currency
The compound interest formula
A = P × (1 + r/n)^(n×t), where P is the starting amount, r the yearly rate, n the number of compounding periods per year and t the number of years. Interest earns interest, so growth speeds up over time.
The rule of 72
Divide 72 by the yearly interest rate to estimate how many years it takes to double your money. At 6%, money doubles in about 12 years; at 9%, in about 8.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is paid only on the original amount. Compound interest is also paid on the interest already earned, so the balance grows faster.
Does more frequent compounding make a big difference?
A little. At 5% for 10 years, 10,000 grows to 16,289 with yearly compounding and 16,470 with monthly compounding.
When are monthly contributions added?
At the end of each month, after that month's interest.