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VeloxCalc

Compound Interest Calculator

See how savings grow with compound interest and regular contributions.

$
%
%
years
Regular contributions
$
Contributions are made

Result

Final balance

$47,526.55

Real final balance (today’s $)
$47,526.55
Initial deposit
$10,000.00
Total contributions
$24,000.00
Total interest
$13,526.55
Real interest earned
$13,526.55
Real annual rate
5%
  • Real (purchasing-power) values use your entered inflation rate; taxes and fees are not included.

Calculated with engine v1.1.0

Nominal final balance $47,526.55 — $47,526.55 in today’s purchasing power; $13,526.55 interest earned.

Year-by-year breakdown
Balance, contributions and interest at the end of each year
YearContributionsInterestBalance
1$2,400.00$567.39$12,967.39
2$4,800.00$1,286.60$16,086.60
3$7,200.00$2,165.39$19,365.39
4$9,600.00$3,211.93$22,811.93
5$12,000.00$4,434.80$26,434.80
6$14,400.00$5,843.03$30,243.03
7$16,800.00$7,446.09$34,246.09
8$19,200.00$9,253.96$38,453.96
9$21,600.00$11,277.11$42,877.11
10$24,000.00$13,526.55$47,526.55

Methodology

Compound interest means you earn interest on your deposit and on the interest it has already earned. The calculator uses the standard compound interest formula for the initial deposit:

A = P × (1 + r ÷ n)n × t

where P is the initial deposit, r the annual interest rate as a decimal (5% = 0.05), n the number of compounding periods per year and t the number of years.

Regular contributions are added on their own schedule — monthly or yearly. To combine any contribution frequency with any compounding frequency, the calculator converts the rate into an equivalent rate per contribution period:

i = (1 + r ÷ n)n ÷ p − 1

where p is the number of contributions per year. The balance then grows period by period: interest at rate i is added, and each contribution is deposited at the end of the period (or at the start, if you choose that option). All amounts are calculated with exact decimals and rounded to the cent only when shown.

Example

You deposit $10,000 at 5% a year, compounded monthly, and add $200 at the end of every month for 10 years.

  • The initial deposit alone grows to 10,000 × (1 + 0.05 ÷ 12)120 = $16,470.09.
  • Your contributions total 120 × $200 = $24,000.
  • Final balance: $47,526.55, of which $13,526.55 is interest.

The year-by-year breakdown below the calculator shows how the interest share grows over time.

Notes and assumptions

  • Constant rate: the rate stays the same for the whole period. Real savings rates and investment returns change, and investments can lose value.
  • No taxes, fees or inflation: interest may be taxable, accounts can charge fees, and inflation reduces what the final balance can buy. None of these are included.
  • Interest is reinvested: all interest stays in the account and keeps compounding.
  • This calculator is for education and planning. It is not financial advice; for decisions about your money, consider talking to a qualified professional.

Frequently asked questions

What is the difference between APR and APY?

APR is the yearly rate without compounding. APY (annual percentage yield) includes the effect of compounding within the year. A 5% rate compounded monthly gives an APY of about 5.12%. Banks in the U.S. advertise APY for savings accounts.

How much does compounding frequency matter?

Less than people expect. Moving from yearly to monthly compounding raises the result slightly; moving from monthly to daily changes it only a little more. The rate and the time you stay invested matter much more.

Does it matter when I make my contributions?

Yes, a little. Contributions at the start of each period earn interest for one more period than contributions at the end, so the final balance is somewhat higher.

What is the Rule of 72?

A quick estimate: divide 72 by the annual rate to see roughly how many years it takes for money to double. At 6%, that is about 12 years. Use the calculator for an exact figure.

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