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Compound Interest Calculator: See How Your Money Grows

A compound interest calculator shows how an initial amount grows when interest is added back to the balance at regular intervals. Enter your starting amount, annual rate, time horizon, and compounding frequency to estimate future value and total interest earned.

1) What the Calculator Does

It models growth when you earn interest on your original principal and on previously-earned interest. More frequent compounding (e.g., monthly vs. annually) generally increases the ending balance for the same APR.

2) Inputs

Provide the following to create a personalized projection.

Input Description
Initial Investment (P) The amount you start with.
Annual Interest Rate (r) Yearly rate of return (as a percentage).
Number of Years (t) How long you’ll keep the money invested.
Compounding Frequency (n) How often interest is added: annually, semi-annually, quarterly, monthly, etc.
Extra Contributions (optional) Regular deposits that accelerate growth (if supported by the widget).

3) How It Works (Formula)

Without extra contributions, the classic formula is:

A = P × (1 + r / n)n × t

  • P = starting principal
  • r = annual rate (decimal)
  • n = compounding periods per year
  • t = years invested
  • A = amount after t years

4) Outputs

Output What It Means
Total Amount (A) Final value including principal and compounded interest.
Interest Earned Total Amount − Initial Investment (− contributions if applicable); the growth from compounding.

5) Practical Use Cases

  • Retirement planning: Estimate future value of today’s savings to set monthly targets.
  • Education funds: Project RESP/529 balances by the time school starts.
  • Account comparison: Test rates and compounding frequencies to choose the best option.

6) FAQ

What’s the difference between APR and APY?
APR is the annual rate without compounding. APY includes compounding and is typically higher when compounding occurs more than once per year.
Does compounding more often always produce a higher return?
Generally yes for the same APR, but the difference can be modest at lower rates or over short periods.
Is this a guarantee of returns?
No. It’s a math-based projection; actual performance depends on the specific investment and market conditions.

Try the Calculator


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