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Compound Interest Calculator

See how your money grows when interest compounds — with contributions, any frequency, and a goal mode.

Updated June 2026 · Editorial standards

Your details

$
$
%
yrs
mos

Enter whole years and any extra months.

Set a goal
Final balance
$144,573
Total contributions
$58,000
Total interest
$86,573

Growth over time

Where your balance comes from

Yearly breakdown

PeriodContributionsInterestBalance
Year 1$2,400$801$13,201
Year 2$2,400$1,033$16,634
Year 3$2,400$1,281$20,315
Year 4$2,400$1,547$24,262
Year 5$2,400$1,832$28,495
Year 6$2,400$2,138$33,033
Year 7$2,400$2,466$37,900
Year 8$2,400$2,818$43,118
Year 9$2,400$3,196$48,714
Year 10$2,400$3,600$54,714
Year 11$2,400$4,034$61,147
Year 12$2,400$4,499$68,046

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By the KalkWise Editorial Team Reviewed for accuracy Updated June 2026

What is the compound interest calculator?

In short

Compound interest is interest earned on both your original money and the interest it has already earned. To calculate it, multiply your starting balance by (1 + r/n) raised to the power of n×t, where r is the annual rate, n is how often it compounds per year, and t is the number of years. Adding regular contributions accelerates growth significantly.

This compound interest calculator shows how a starting amount grows when interest is repeatedly added back to the balance. You can include regular contributions, choose any compounding frequency, set the time in years and months, and switch on goal mode to find out when you'll hit a target.

How to use this calculator

  1. 1Enter your starting amount (principal).
  2. 2Add a contribution and choose how often you'll add it.
  3. 3Set the annual interest rate and how often interest compounds.
  4. 4Choose the time period in years and months.
  5. 5Optionally turn on "Set a goal" to see when you'll reach a target.

The formula

FV=P(1+rn)nt+PMT×[(1+rn)nt−1rn]
The first term grows your starting amount; the second term adds up the future value of every contribution. Together they give your final balance.
FV
— Future value (final balance)
P
— Starting principal
PMT
— Periodic contribution
r
— Annual interest rate (decimal)
n
— Compounding periods per year
t
— Number of years

KalkWise simulates each month individually so that contributions, compounding frequency, and partial years are all handled precisely.

Worked example

The scenario

Start with $10,000, add $200 every month, earn 7% compounded monthly, for 20 years.

gives

The result

Your balance grows to about $204,000 — roughly $58,000 in contributions plus $10,000 principal, with the remaining ~$136,000 coming from compound interest.

Common use cases

  • Planning long-term savings or an investment account
  • Comparing the effect of different interest rates
  • Seeing how monthly contributions accelerate growth
  • Understanding the long-term cost of compounding on debt

Limitations & assumptions

  • Assumes a constant interest rate for the whole period — real returns vary year to year.
  • Does not account for taxes on interest or capital gains.
  • Ignores inflation; use the Inflation Calculator to see real purchasing power.

Frequently asked questions

Compound interest is interest calculated on both your original principal and all accumulated interest. For example, $10,000 at 7% compounded monthly grows to ~$20,097 after 10 years — that's $10,097 in pure interest. With $200/month added, that same account reaches ~$55,000.

Disclaimer: KalkWise calculators are provided for general informational and educational purposes only and do not constitute financial, investment, tax, or legal advice. Results are estimates based on the figures you enter and the assumptions described above. Actual outcomes will vary. Consult a qualified professional before making financial decisions.