Compound Interest Calculator — Free Investment Growth Calculator

Use this compound interest calculator to project exactly how an investment or savings account grows over time. Enter your starting principal, annual interest rate, compounding frequency, and duration to see the total balance and how much of it is earned interest.

Why use this Compound Interest Calculator?

  • Supports daily, monthly, quarterly, and annual compounding
  • Shows total balance and interest earned separately
  • Optional regular contribution field to model monthly savings
  • Instant results — all computation runs in your browser

How to use the Compound Interest Calculator

  1. Enter your principal: Type the initial amount you're investing or depositing, for example $5,000.
  2. Set the annual interest rate: Enter the yearly rate your account or investment earns, such as 7% for a long-term stock index assumption.
  3. Choose compounding frequency: Select how often interest is compounded — monthly is common for savings accounts, daily for some high-yield accounts.
  4. Enter the time period: Type the number of years you plan to hold the investment, then read the projected total balance and interest earned.

Frequently Asked Questions

What is the compound interest formula?

A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual interest rate as a decimal, n is the number of compounding periods per year, and t is the time in years. For example, $10,000 at 6% compounded monthly for 10 years: A = 10,000 × (1 + 0.06/12)^(12×10) ≈ $18,194.

How does compounding frequency affect growth?

More frequent compounding means interest is calculated on a slightly larger balance each period, producing more total growth. Daily compounding yields slightly more than monthly, which yields more than annual — though the difference is modest compared to the rate and time period.

What is the Rule of 72?

The Rule of 72 is a quick mental shortcut: divide 72 by the annual interest rate to estimate how many years it takes to double your money. At 6% annual interest, your money doubles in roughly 72 ÷ 6 = 12 years. It's an approximation; this calculator gives the exact figure.

What's the difference between simple and compound interest?

Simple interest is calculated only on the original principal each period. Compound interest is calculated on the principal plus all previously accumulated interest, so the balance grows faster over time. Over long periods, the gap between the two is enormous — this is why compounding is so powerful.

Can I use this calculator for a savings account?

Yes. Enter your initial deposit as the principal, your account's APY as the rate (choose monthly compounding for most savings accounts), and how many years you plan to save. If you make regular deposits, enter that amount in the monthly contribution field to model realistic savings growth.

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