Compound Interest Calculator

See how savings grow with compound interest and regular monthly contributions, at any compounding frequency.

$
$
%
Future value
$54,713.58

Interest makes up 37.9% of the final balance.

Balance over time
DepositsInterest
$0$10K$20K$30K$40K$50K$60K0246810Years
Total deposits
$34,000.00
Interest earned
$20,713.58
Effective annual rate (APY)
7.229%
Final balance
Deposits: $34,000 (62.1%)Interest: $20,714 (37.9%)38%is growth
  • Deposits$34,00062.1%
  • Interest$20,71437.9%
Show the working
  1. Effective annual rate = 7.229% (7% compounded 12× a year)
  2. Initial deposit grows to $10,000.00 × 2.009661 = $20,096.61
  3. 120 monthly deposits of $200.00 grow to $34,616.96
  4. Future value = $54,713.58

Runs entirely in your browser. Nothing you enter is uploaded.

Formula

A = P(1 + r/k)^(k·t) (lump sum)With monthly deposits C: A = P·g^n + C·(g^n − 1) ÷ (g − 1)g = (1 + r/k)^(k/12) is the monthly growth factor, n = monthsContinuous compounding: A = P·e^(r·t)

How it works

Compound interest means you earn interest on your earlier interest, not just on the money you put in. In the early years the effect is small, but it accelerates: at 7% a year, money roughly doubles every ten years, so the second decade adds twice as much as the first.

Compounding frequency is how often interest is credited. More frequent compounding gives a slightly higher effective annual rate (APY) — 5% compounded monthly is 5.116% a year — but the difference between monthly and daily is tiny. Time and the rate itself matter far more.

Regular contributions are often the biggest driver for savers. This calculator assumes each monthly deposit is made at the end of the month and grows at the same rate as the balance. Real investment returns vary year to year; use a conservative rate for planning.

Frequently asked questions

What is the rule of 72?

Divide 72 by the annual interest rate to estimate how many years it takes to double your money. At 6%, that is about 12 years. It is a quick approximation that works well for rates between about 4% and 12%.

What is the difference between APR and APY?

APR is the nominal yearly rate before compounding. APY includes the effect of compounding within the year, so it is the rate you actually earn. Banks advertise savings with APY because it is the larger number.

Does this account for taxes or inflation?

No. Interest in a regular account is usually taxable each year, and inflation reduces what the final balance can buy. Use the inflation calculator to convert the result into today's dollars.

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