Compound Interest Calculator
See how your investments grow over time with compound interest and regular contributions.
Investment Details
Growth Results
Understanding Compound Interest
Compound interest is often called "interest on interest" - it's the powerful concept where you earn interest not only on your initial principal, but also on the accumulated interest from previous periods. This compounding effect is what makes long-term investing so powerful.
Compound Interest Formula (without contributions): A = P(1 + r/n)^(nt)
Where A is the future value, P is the principal, r is the annual interest rate, n is the number of times interest compounds per year, and t is the number of years.
The Power of Compounding
The frequency of compounding matters - more frequent compounding (daily vs. annually) results in slightly more growth. However, time is the most important factor. Starting early, even with small amounts, can lead to significant growth over decades due to compounding.
Adding Regular Contributions
Making regular contributions (like monthly deposits) dramatically accelerates your growth. These contributions also compound over time, multiplying their impact. This strategy, often called dollar-cost averaging with growth, is fundamental to long-term wealth building.
Real-World Applications
Compound interest applies to savings accounts, certificates of deposit (CDs), retirement accounts (401(k), IRA), and investment portfolios. Understanding it helps you set realistic goals and appreciate the value of starting early and staying consistent.
Important Notes
These are hypothetical projections. Actual investment returns vary and may be negative. Taxes, fees, and inflation are not accounted for in this basic calculation. Past performance doesn't guarantee future results. Consult a financial professional for personalized advice.
Worked Example: Starting With $10,000
Suppose you invest $10,000 at an average annual return of 7%, compounded monthly, and you add $200 every month for 20 years. In the calculator above, enter 10000 as the initial principal, 7 as the annual interest rate, 20 as the time period, choose monthly compounding, and enter 200 as the monthly contribution.
Your total contributions over 20 years are $10,000 plus 240 payments of $200, which is $58,000. The calculator shows a final balance of about $144,573, so roughly $86,573 of it is interest earned. That growth on top of your contributions is the effect of compounding. Try changing the time period to 10 and then 30 years to see how much more the balance grows when you give it more time.
Why Starting Early Matters
Compounding rewards time. Money invested earlier has more years to earn returns on its own earlier returns. Someone who invests a smaller amount for 30 years can end up with more than someone who invests a larger amount for only 15 years. Run both scenarios in the calculator to compare them.
The Rule of 72
A quick way to estimate how long it takes to double your money is to divide 72 by the annual interest rate. At 6%, money doubles in roughly 12 years. At 9%, it takes roughly 8 years. This is an approximation, but it is useful for quick mental checks.
Compounding Frequency
Interest can be compounded annually, quarterly, monthly, or daily. More frequent compounding produces slightly more growth, but the difference is usually small compared with the effect of the interest rate and the length of time.
Frequently Asked Questions
What is the difference between simple and compound interest?
Simple interest is calculated only on the original amount. Compound interest is calculated on the original amount plus the interest already earned, so growth speeds up over time.
What interest rate should I assume?
Returns are never guaranteed. Savings accounts usually pay lower rates, while long-term investments in stocks have historically had higher but less predictable returns. It is wise to test several rates, including conservative ones.
Does inflation affect these results?
Yes. The calculator shows nominal values. Because prices tend to rise over time, a future balance will buy less than the same amount does today.
Are taxes and fees included?
No. Investment fees, account fees, and taxes reduce your real return. Consider them when comparing accounts or funds.
How do regular contributions help?
Each contribution starts earning returns from the day it is added. Even modest monthly deposits can add up substantially over many years.