FinanceCalco

Compound Interest Calculator

Built & reviewed by the FinanceCalco editorial teamHow we test calculatorsUpdated June 2026

See how your money grows with compound interest and regular monthly contributions. Set your starting amount, monthly deposit, rate, time frame, and compounding frequency — the final balance and interest earned update instantly, and you can export the numbers or share them with a link.

Final balance

$144,572.72

Total contributed
$58,000.00
Interest earned
$86,572.72
$
$
%
yr

Growth over time

$0$50K$100K$150K$200K0y3y7y10y13y17y20y
ContributionsInterest
$144.6KFinal balance
Contributions$58,000.00Interest earned$86,572.72
How this is calculatedmethodology

The initial principal compounds at your selected frequency, while monthly contributions are added and compounded monthly. Interest earned is the final balance minus everything you put in.

FV = P(1+rₙ)^(n·t) + m·((1+rₘ)^(12·t) − 1)/rₘ
P
Initial principal.
m
Monthly contribution.
rₙ
Periodic rate = annual rate ÷ compounding periods per year.
rₘ
Monthly rate = annual rate ÷ 12.
n
Compounding periods per year.
t
Number of years.
  • Selected compounding frequency
  • Contributions compounded monthly

How to use the compound interest calculator

  1. Enter your starting principal and any monthly contribution.
  2. Set the annual interest rate, the number of years, and how often interest compounds.
  3. See your final balance split into contributions and interest earned.

TipTime matters most. Starting a few years earlier often beats contributing more later.

How to use the compound interest calculator

Enter your initial principal — the amount you’re starting with — and the monthly contribution you plan to add each month. Set the annual interest rate you expect to earn, the number of years you’ll stay invested, and how often interest compounds. The large readout shows your projected final balance, and the cells below split it into the total you contributed and the interest earned on top.

Try changing one input at a time to see what moves the needle most. Raising the monthly contribution, extending the time frame, or earning a higher rate all increase the final balance — usually by far more than you’d expect, because the growth compounds. Use the export buttons to download the summary as CSV or Excel, print it to PDF, or copy a link that reopens the calculator with your exact numbers.

How compound interest works

With compound interest, each period’s interest is added to your balance, and the next period earns interest on that larger total. Your principal grows by the formula FV = P·(1 + r)n, where P is the principal, r is the rate per compounding period, and n is the number of periods. Monthly contributions are added along the way and compound from the moment they’re invested, so money you put in early has the most time to grow.

The two biggest levers are time and rate. Because growth is exponential, the last few years of a long horizon add the most absolute dollars, and a small difference in rate can mean a large difference in the final balance. These projections are nominal and before tax and inflation, so treat them as an educational illustration of growth rather than a guaranteed outcome.

Estimates for education only — not investment or financial advice. Actual returns vary, are not guaranteed, and may be reduced by fees, taxes, and inflation.

Frequently asked questions

What is compound interest?

Compound interest is interest earned on both your original money and the interest it has already earned. Instead of paying out only on your initial deposit, each period’s interest is added to the balance, so the next period earns interest on a larger amount. Over many years this snowball effect is what makes long-term saving and investing so powerful.

How does compounding frequency change my result?

The more often interest is compounded — daily versus annually, for example — the more often earned interest starts earning its own interest, so the final balance is slightly higher. The difference is modest at low rates and short horizons but grows with higher rates and longer time frames. This calculator lets you compare annual, quarterly, monthly, and daily compounding on your principal.

Does this account for taxes or inflation?

No. The figures here are nominal, pre-tax growth. Real-world returns are reduced by taxes on interest or gains and by inflation, which erodes the purchasing power of your final balance. Treat the result as an educational projection of gross growth, not a guaranteed or after-tax outcome.

Related guides

All guides →