Compound Interest Calculator
See exactly how compound interest grows your savings over time. Add monthly contributions and compare compounding frequencies.
How to use Compound Interest Calculator
This compound interest calculator shows how a lump sum and regular contributions grow over time as interest earns interest. Set your starting balance, monthly or annual deposits, an expected rate and the compounding frequency to see the future value, total contributions and total interest earned — plus a growth chart that makes the power of compounding visible. It is the single most useful tool for understanding long-term saving and investing.
- Enter your starting principal (or 0 if starting from scratch).
- Add a regular contribution and choose how often you deposit.
- Set the expected annual interest/return rate.
- Choose the compounding frequency (daily, monthly, annually).
- Set the number of years and review the future value and growth chart.
Your data never leaves your device — 100% private processing.
How compound interest works
Compound interest is calculated with A = P(1 + r/n)^(nt), where P is the principal, r is the annual rate, n is the number of times interest compounds per year and t is the number of years. The key difference from simple interest is that each period’s interest is added to the balance, so the next period earns interest on a larger amount. Over long horizons this snowball effect dominates — most of a 30-year balance is interest, not contributions.
Why frequency and time matter
More frequent compounding (daily vs annually) increases the effective yield slightly, but time is the far more powerful lever. Starting ten years earlier typically beats contributing more later, because the earliest dollars compound the longest. This is why financial planners stress beginning to invest as early as possible, even with small amounts.
| Years | Future value | Interest earned |
|---|---|---|
| 10 years | $19,672 | $9,672 |
| 20 years | $38,697 | $28,697 |
| 30 years | $76,123 | $66,123 |
Worked examples
Lump sum
Inputs: $10,000 · 7% · 30 yr · monthly
Result: ~$81,165 future value
With $300/mo added
Inputs: $10,000 + $300/mo · 7% · 30 yr
Result: ~$444,000 future value
Glossary
- Principal
- The initial amount you start with before any interest.
- Compounding frequency
- How often earned interest is added to the balance (daily, monthly, yearly).
- APY
- Annual percentage yield — the real rate of return once compounding is included.
- Future value
- What your balance is projected to be worth at the end of the period.
Related reading
Frequently Asked Questions
Get weekly tool tips & updates
New tools, power-user tips, and productivity hacks — delivered free every Friday.
No spam, ever. Unsubscribe with one click.
Why use Compound Interest Calculator?
- Transparent formulas so you understand every calculation
- Supports multiple currencies and regional tax rules
- Saves you from spreadsheet errors with validated inputs
- Shareable results for discussions with advisors or partners
Common use cases
- Calculate how long to pay off a credit card balance
- Model different mortgage scenarios before house hunting
- Forecast investment growth with compound interest
- Break even analysis for a new product or service
- Compare net salary after tax across different countries
Related Finance
Mortgage Calculator
Calculate your monthly mortgage payment, total interest, and see a full amortization schedule. Free online mortgage calculator.
Investment Calculator
Calculate investment returns, ROI, and compound growth. Enter initial amount, rate, and time to see final value and year-by-year growth.
Retirement Calculator
Calculate how much you need to retire. Enter your age, savings, and contributions to see your projected retirement nest egg and monthly income.
Loan Calculator
Calculate your loan monthly payment, total interest, and payoff. Compare rates and terms instantly with this free online personal loan calculator.
Tip Calculator
Calculate tip amount and split the bill between multiple people. Choose custom tip percentage and see per-person totals.
Discount Calculator
Calculate discounted prices, find what percentage off an item is, or find the original price. Free online discount calculator.
Explore all Finance.