CALCULATORS
Compound Interest Calculator
Project account growth with an initial amount, monthly contributions, rate and time period.
Quick answer: Enter the assumptions and review the estimated balance. Actual returns are not guaranteed.
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How to use Compound Interest Calculator
- Enter your starting amountAdd the initial deposit and any regular contribution.
- Set rate, time and compoundingChoose the annual rate, number of years and how often interest compounds.
- Read the projectionCompare the final balance with your total contributions to see the growth from interest.
About this tool
Compound interest means earning interest on your earlier interest, which is why time matters so much. Enter a starting amount, regular contributions, the annual return and the number of years to see the projected balance.
Common uses: Compare savings scenarios, recurring contributions and long-term growth assumptions for personal planning or classroom examples.
Practical example: Change one assumption at a time—starting amount, monthly contribution, annual return or years—so you can see which factor drives the projection.
Important limitation: The projection assumes the inputs and compounding pattern remain stable. Actual returns, fees, taxes and inflation can materially change outcomes.
Calculations happen in your browser; the figures you type are not uploaded. Read the privacy information.
How it works
Each period, interest is calculated on the current balance (including past interest) and contributions are added, so growth accelerates over time.
Real-world uses
- Projecting retirement savings
- Comparing two interest rates
- Showing how early saving matters
Reading a projection realistically
The biggest levers are time and consistency, not the compounding frequency. Daily versus monthly compounding changes the result by a little, while an extra ten years or a higher monthly contribution changes it by a lot. Change one input at a time to see which one drives the outcome.
Use the inflation assumption to see the projection in today’s money. A balance of 100,000 in twenty years buys less than 100,000 does today, so the real value can be noticeably lower than the nominal figure. The yearly breakdown shows your contributions and interest separately so you can see how much of the growth is yours and how much is earned.
The projection assumes a steady return. Real investments move up and down, can lose money, and have fees and taxes. Treat the figure as an illustration of the maths, not a forecast.
Tips for better results
- Formula: A = P(1 + r/n)^(nt). More frequent compounding helps, but time and rate matter far more.
- The Rule of 72 estimates doubling time: 72 ÷ rate (%) years.
- Remember fees, taxes and inflation; real returns are lower than nominal ones.
Frequently asked questions
Does the result guarantee future growth?
No. It is a mathematical projection based on the assumptions you enter, not a forecast or financial recommendation.
Why do regular contributions matter?
Contributions add new principal over time, so their timing and compounding period affect the final projection.
Are my calculations uploaded?
Calculations happen in your browser; the figures you type are not uploaded.
Does the result guarantee growth?
No. It assumes a constant rate. Real returns vary and can be negative.
Monthly vs daily compounding?
Daily compounding yields slightly more, but the difference is small compared with changing the rate or the time horizon.
What is the Rule of 72?
Divide 72 by the annual return in percent to estimate how many years it takes to double. At 6 percent, money doubles in about 12 years.
Does compounding monthly beat compounding annually?
Slightly, because interest is added sooner. The difference is small compared with changing the rate, the years or the contribution.
Can I include regular deposits?
Yes. Set a contribution amount and choose monthly or annual deposits. The projection adds them to the balance as time passes.