Compound Interest Calculator
Calculate compound interest with different compounding frequencies. See year-by-year growth and add regular contributions.
Compound Interest Formula
Regular Contributions (Optional)
Advanced Options
Final Results
Detailed Metrics
Understanding Compound Interest
- Compound interest means earning interest on your interest
- More frequent compounding = more growth (daily > monthly > annually)
- Regular contributions dramatically increase final value
- Time is your best friend - start early for maximum benefit
- The "Rule of 72": Years to double = 72 ÷ interest rate
This compound interest calculator shows how your money grows over time. Choose from multiple compounding frequencies (daily, monthly, quarterly, annually), add regular contributions, and see detailed year-by-year projections. Perfect for planning investments, savings accounts, and understanding the power of compound interest.
Compound interest means earning returns on both your original principal and the interest already accumulated. The standard formula is A = P(1 + r/n)^(nt), where P is the principal, r is the annual rate as a decimal, n is compounding periods per year, and t is time in years. A continuously compounding variant uses A = Pe^(rt). The difference between annual and daily compounding on the same stated rate is the effective annual yield: at 7% nominal, monthly compounding gives a 7.229% effective rate, while daily compounding gives 7.250%.
This calculator adds regular contributions on top of the principal, which is where long-term projections become most striking. A $10,000 lump sum at 7% over 20 years grows to about $38,700. Add $500 per month and the final balance climbs to roughly $284,000 - the monthly deposits account for more than half the total. The Scenarios tab lets you compare what happens at 50% fewer contributions, the current amount, 50% more, and double to see how contribution level affects the outcome.
Advanced options let you enter an inflation rate to see the real purchasing-power value in today's dollars, and a tax rate on interest to model a taxable brokerage account. The Breakdown tab shows a year-by-year table with start balance, contributions, interest earned, and end balance for every year in the projection period.
- 1
Enter principal, rate, and term
Type the starting amount, annual interest rate, and number of years. Pick a compounding frequency from daily to annually or continuously.
- 2
Add optional contributions
Enter a regular contribution amount and choose monthly, quarterly, or annual frequency. The final balance recalculates immediately.
- 3
Explore the result tabs
Switch between Metrics, Comparisons, Scenarios, and Breakdown to see effective rate, inflation-adjusted value, what-if scenarios, and the year-by-year growth table.
Retirement savings planning
Model a $500/month contribution to a retirement account at 7% over 30 years to see the projected balance at retirement.
Comparing savings accounts
Enter two different APYs to compare how much extra a high-yield account earns over a traditional savings account over five years.
Understanding compounding frequency
Compare annual versus daily compounding at the same stated rate to see the difference in effective yield over a long horizon.
Inflation impact on investments
Enter a 3% inflation rate alongside your investment return to see the real purchasing-power value of your projected balance.
What compounding frequencies are supported?
Annually, semi-annually, quarterly, monthly, weekly, daily, and continuously. Continuous compounding uses the formula A = Pe^(rt) rather than the discrete formula.
How is the contribution handled mathematically?
Contributions are treated as a monthly equivalent and compounded separately using a future-value-of-annuity formula, then added to the principal's growth. The year-by-year table simulates month by month for accuracy.
What does the Effective Annual Rate mean?
It is the actual yearly return after accounting for intra-year compounding, also called APY. A 7% nominal rate compounding monthly has a 7.229% effective annual rate.
Does this calculator save my inputs?
Compounding frequency and contribution frequency are saved between sessions. Principal, rate, years, and contribution amount are not persisted and reset to defaults on a new visit.
Is any of my financial data transmitted to a server?
No. All calculations run locally in your browser. No numbers you enter are sent anywhere, and the page works fully offline once loaded.