CAGR Calculator
Calculate compound annual growth rate from a starting value, ending value, and time in years.
Open toolCompound Interest Calculator
Estimate compound interest with monthly contributions, a starting balance, and a fixed annual rate. Compare total deposits and estimated growth under your assumptions.
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How Compound Interest Calculator works
Equivalent monthly growth is applied before each month-end contribution.
The selected compound frequency is converted into an equivalent monthly growth rate. Each modelled month applies that rate to the balance, then adds the contribution at month end. Years are rounded to full months.
Assumes a fixed nominal annual rate, contributions at each month end, and no taxes or fees. Results are estimates, not investment returns.
Reference: Investor.gov: Compound Interest Calculator.
How to use Compound Interest Calculator
Keep the deposit schedule separate from the compounding frequency when preparing the inputs.
Configure the balance and growth assumptions
Enter the starting amount, monthly contribution, annual rate, and years, then choose compound frequency. Use one fixed rate for the scenario. The contribution is monthly even when the chosen growth frequency is daily, quarterly, or annual.
Starting amount
Calculate the modelled future value
Select Calculate to read the estimated future value. The tool applies the equivalent monthly growth rate and adds each contribution at month end. Compare a second scenario by changing one input and retaining the others as a clear baseline.
$34,000.00
Separate deposits from interest
Review Total deposited, Estimated interest, and Months modelled. Future value includes the money contributed, so it is not all interest. Years are rounded to full months, and the fixed-rate model excludes taxes and fees rather than predicting actual returns.
Total deposited
Compare compound interest with monthly contributions
Change one assumption at a time to see what caused the estimated balance to move.
Compare monthly contribution amounts
Hold the starting balance, rate, time and frequency fixed while changing the monthly contribution. Compare both total deposited and estimated interest. A higher final balance can come from adding more money as well as from growth on that money.
Inspect deposit timing assumptions
Use the output as a model of deposits made at month end. If a separate spreadsheet adds deposits at month start, its balance may differ even with the same contribution amount. Align the timing before comparing those calculations.
Check compound growth at zero interest
Set the annual rate to zero to isolate deposits. A hypothetical $1,000 starting balance with $100 deposited monthly for one year gives $2,200. This arithmetic check makes the number of contributions visible without relying on a growth assumption.
Future value, deposits, and estimated compound interest
Separate contributions from estimated interest when comparing future balances.
The duration in years is converted to a whole number of months for the calculation. Read the months modelled line when entering a fractional year, especially when comparing it with another model using exact days.
Estimated interest is the final balance minus the starting amount and later deposits. It assumes the entered rate stays fixed. Taxes, fees and changing returns are absent, so the output cannot promise an investment outcome.
Compare schedules before comparing balances
Review rate, timing, and month-count assumptions before using the model.
Different tools may use different rate conventions or contribution timing. Check the nominal rate, selected frequency and monthly deposit basis before attributing a difference to rounding. Keep those assumptions with a saved result.
Enter a monthly contribution in the monthly field; an annual contribution entered there would be repeated each month. This calculator does not handle irregular deposits, withdrawals or a changing rate schedule, so those cash flows need a separate model.
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Compound Interest Calculator: common questions
Answers about using Compound Interest Calculator and understanding its results.
When are contributions added?
The monthly contribution is added at the end of each month.
Is the rate guaranteed?
No. This calculator holds the rate constant only to illustrate compounding.
Does changing frequency change deposit timing?
No. Contributions still enter at the end of each month. Frequency changes the equivalent monthly rate used for growth.
Are taxes and account fees included?
No. The result uses a fixed entered rate without taxes or fees. It is a modelled estimate rather than a promised investment return.