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Compound Interest Calculator
Project investment growth from a starting balance, recurring contributions, annual return, compounding frequency, and contribution increases.
Investment plan
Growth assumptions
Balance over time
Yearly growth
Growth mix
Year-by-year projection
| Year | Deposits | Interest | Year-end balance | Interest share |
|---|
Interpret your compound interest estimate
The future balance shows what the account could grow to if the return, contributions, compounding frequency, and timing assumptions stay constant.
Inputs that matter most
- Starting balance: money that begins compounding immediately.
- Monthly contribution: new money added throughout the projection.
- Annual return: the constant rate used for the projection.
- Years to grow: longer timelines give compounding more room to work.
Common mistakes
- Treating a constant return as a market forecast.
- Ignoring taxes, fees, and inflation when comparing future dollars.
- Forgetting that contribution timing changes how long each deposit compounds.
- Assuming a high return without testing lower-return scenarios.
When this estimate can be misleading
This estimate can be misleading for volatile investments, taxable accounts, accounts with fees, or plans where contributions will change more than the yearly increase entered.
Scenarios to try
- Lower the annual return to see a conservative case.
- Increase monthly contributions to test a higher savings rate.
- Try shorter and longer timelines to see how time affects interest earned.
- Add a yearly contribution increase to model raising savings over time.
Next-step utilities
How to use this compound interest calculator
Estimate how savings or investments may grow with recurring contributions and compound returns.
- Enter your current balance and the amount you plan to add each month.
- Set the annual return, number of years, compounding frequency, and contribution timing.
- Add a yearly contribution increase if you expect to raise your monthly contribution over time.
- Try lower and higher return assumptions instead of treating one result as a forecast.
- Review the future balance, interest earned, charts, and year-by-year projection.
Compound Interest Calculator features
- Project compound growth from a starting balance and monthly contributions.
- Compare daily, monthly, quarterly, and annual compounding.
- Choose beginning-of-month or end-of-month contribution timing.
- Model yearly contribution increases.
- See total deposits, interest earned, growth multiple, and interest share.
- Visualize balance growth against total deposits.
- Chart yearly contributions and interest earned.
- Inspect a year-by-year projection table.
What compound interest shows
Compound interest means returns can earn returns. Over long timelines, that can make the interest portion of the final balance much larger than the amount deposited.
The chart compares total deposits with the projected balance so you can see when compounding starts doing more of the work.
Small changes to return, time, and monthly contributions can have a large effect, so it is useful to test multiple scenarios instead of relying on one estimate.
The future balance is shown in nominal dollars. It does not adjust for inflation, taxes, account fees, contribution limits, or market volatility unless you lower the return assumption to approximate those effects.
Contribution timing matters most over long periods or with large deposits. Beginning-of-month contributions have a little more time to compound than end-of-month contributions.
Compound interest formula
The calculator converts the annual return and selected compounding frequency into an effective monthly growth rate, then simulates each month of deposits and interest.
r_m = (1 + r / n)^{n / 12} - 1
r is the annual return and n is the number of compounding periods per year.
After calculating the effective monthly rate, the projection steps through each month, applies contributions based on the selected timing, grows the balance, and increases future contributions when a yearly increase is entered.
Compound interest calculator FAQ
Does this include taxes or fees?
No. This calculator shows a simple pre-tax, pre-fee projection. For taxable or fee-heavy accounts, reduce the annual return to approximate those costs.
Why does contribution timing matter?
A beginning-of-month contribution is invested for one extra month compared with an end-of-month contribution, so it earns slightly more interest over time.
Is the annual return guaranteed?
No. The annual return is an assumption for planning. Real investments can rise, fall, and compound unevenly from year to year.
Does this account for inflation?
No. Results are nominal dollars. To think in today's purchasing power, compare the projection with a lower inflation-adjusted return or subtract an inflation assumption separately.
Why test more than one return?
A single return can make a plan look more certain than it is. Testing conservative, moderate, and optimistic returns shows how sensitive the outcome is to market assumptions.
Use a range of growth assumptions
Separate the mechanics of compounding from the uncertainty of investing. A savings account may credit a stated rate that can change, while an investment portfolio has uneven returns and can lose value. The smooth line in a projection is a mathematical path, not a forecast of yearly account balances.
Run a low, middle, and high return case. Keep the contribution amount and time horizon identical so the effect of the return assumption is clear. The Investor.gov compound interest calculator likewise treats the rate as an estimate and offers a variance range for comparison.
Check whether the entered rate is nominal or effective and whether the contribution occurs at the beginning or end of each period. Those details matter more as balances grow. This tool uses the selected compounding and contribution settings, but it does not deduct taxes, investment expenses, withdrawal fees, or purchasing-power loss unless an input explicitly accounts for them.
Inflation can make a large future balance buy less than the same amount today. Compare the nominal result with an inflation-adjusted return when planning a distant goal. Revisit the projection at least yearly with the actual balance and contribution rate; changing the savings amount is often more controllable than choosing a higher expected return.
Contribution timing matters when cash flows are large. Money added at the beginning of a period has one more period to grow than money added at the end. Real payroll and bank transfers may occur twice monthly, every two weeks, or on changing dates, so the account will not match a simplified monthly projection exactly. Use the same timing convention across scenarios, and judge progress from the long-term range rather than a small month-to-month variance.
If the goal has a fixed date, work backward from the amount needed and test whether the required contribution fits the budget. If it does not, the honest choices are usually more time, a lower target, or a higher contribution—not simply assuming a higher return. Keep short-term money separate from investments whose value may be down when the money is needed.
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