Compound Interest Calculator

The Compound Interest Calculator projects how an investment grows when interest is reinvested, using the standard formula A = P(1 + r/n)ⁿᵗ plus an annuity term for optional monthly contributions. You provide an initial principal, an annual rate, a compounding frequency — Annually, Quarterly, Monthly, or Daily — and a number of years, then optionally add a monthly contribution. The tool immediately shows your projected balance, total contributions, and interest earned, so you can see at a glance how much of the final figure is money you saved and how much is growth doing the work. Contributions are applied at the end of each period, a conservative convention the page states openly. That frequency dropdown is the key to the tool's usefulness: the same 7 percent rate compounds to meaningfully different balances at annual versus daily frequency, and the gap widens with every passing year. Savers use it to model retirement accounts, compare savings products, and test how a small monthly deposit accelerates a long-term goal. Because every result is recalculated live and the formula is printed on the page, it doubles as a transparent compound interest growth projection tool for rough planning — with the usual caveat that past returns never guarantee future ones.

1. 1

   Enter the starting balance in the Initial principal field.

2. 2

   Set the Annual rate as a percentage, such as 7 for seven percent.

3. 3

   Pick a Compounding frequency from the dropdown: Annually, Quarterly, Monthly, or Daily.

4. 4

   Enter the Years you plan to hold the investment, then optionally a Monthly contribution.

5. 5

   Read the Projected balance, plus Final amount, Total contributions, and Interest earned — all live.

• Projecting how a retirement account grows with a $200 monthly contribution over a decade.
• Comparing a savings account that compounds daily against one that compounds quarterly.
• Modelling a college fund with a fixed deposit and monthly top-ups.
• Separating growth from deposits in an investment review.
• Stress-testing how a lower rate would shrink a long-term goal.
• Estimating an emergency fund target with zero additional deposits.

• Contributions are treated as made at the end of each period, so real-world results may differ slightly.
• The model ignores fees, taxes, and inflation — deduct those to see net, inflation-adjusted growth.
• Use a realistic long-run rate rather than last year's return; compounding magnifies overestimation.
• Compare the same scenario across frequencies to understand how much the dropdown choice moves the outcome.
• Do not treat the projection as a guarantee; markets vary and past performance is not future results.
• For a savings account, enter the nominal or APY rate as published — the tool applies it as a flat annual rate.

• Run the same scenario at Monthly and Daily frequency — the small difference compounds into real money.
• The three stats split your final balance into deposits and growth, which is great for financial reviews.
• Leave Monthly contribution at 0 to model a one-time deposit cleanly.
• Raise the Years by five and watch interest earned accelerate — that is compounding doing its job.