How is compound interest calculated?

The standard formula is A = P(1 + r/n)^(nt), where P is the principal, r is the annual rate as a decimal, n is how many times a year interest compounds, and t is the number of years. This calculator applies that formula and, if you add a monthly contribution, also future-values each deposit to the end of the term.

What is the difference between simple and compound interest?

Simple interest is paid only on your original principal, so it grows in a straight line. Compound interest is paid on your principal plus all previously earned interest, so the balance grows faster and faster over time. The more often it compounds, the bigger the effect.

Is this compound interest calculator private?

Yes. Every calculation runs entirely in your browser with JavaScript. The numbers you enter are never uploaded, logged or stored anywhere, and there are no accounts or tracking of your inputs.

Compound Interest Calculator — Future Value & Growth

See how your money grows. Enter a starting amount, an annual rate, the number ofyears and how often interest compounds — add an optional monthly contribution — and watch the future value update live.

How to use it

Enter your starting amount. This is the principal you begin with, e.g. 10000. The currency doesn’t matter — just type the number.
Set the annual interest rate. Type the yearly rate as a percent, e.g. 7 for 7%. Decimals like 4.5 are fine.
Choose the number of years you want the money to grow, and pick how often interest compounds — annually, semi-annually, quarterly, monthly or daily.
Optionally add a monthly contribution. If you plan to add a fixed amount every month, enter it and the calculator folds those deposits into the total.
Read the results. The cards show your future value, the total you deposited, and the total interest earned on top of your deposits.

Every card recalculates the instant you change a number, so you can experiment with rates, terms and contributions without pressing a button.

The compound interest formula

Compound interest is interest earned on interest. The lump-sum part uses the classic formulaA = P(1 + r/n)^nt, where P is your principal, r is the annual rate as a decimal,n is the number of compounding periods per year, and t is the number of years. For example, 10,000 at 7% compounded monthly for 10 years grows to about 10,000 × (1 + 0.07/12)¹²⁰ ≈ 20,097 — it roughly doubles, all from reinvested interest. When you add a monthly contribution, each deposit is grown to the end of the term and summed on top, which is why steady contributions can dwarf the starting balance over long periods.

Why compounding frequency matters

The more often interest compounds, the more often you earn interest on your interest, so the final balance is slightly higher. The same 7% rate produces a little more compounded daily than annually. The jump from annual to monthly is meaningful; from monthly to daily the difference is usually small. Two things matter far more than frequency, though: time andregular contributions. Thanks to exponential growth, starting a few years earlier — or adding a modest amount every month — typically beats chasing a marginally higher compounding frequency.

Is it private?

Yes. The Compound Interest Calculator is plain JavaScript that runs entirely inside your browser tab. The amounts, rates and contributions you type are never uploaded, logged or stored anywhere — there are no accounts and no tracking of your inputs. Once the page has loaded you can even use it offline.

Frequently asked questions

Does it account for inflation or taxes?

No. It shows nominal growth only. Real purchasing power will be lower after inflation, and interest may be taxable depending on where you live and the account type. Treat the results as a pre-tax, pre-inflation estimate.

When are the monthly contributions added?

Each contribution is treated as deposited at the end of the month and then grown until the end of the term. This is the common “ordinary annuity” convention, which gives a slightly more conservative figure than depositing at the start of each month.

What currency does it use?

It is currency-neutral. Whatever number you enter is treated as a plain amount, so the future value, deposits and interest all come out in the same currency you typed — dollars, euros, pounds, rupees or anything else.

Results are estimates rounded for display; for real financial decisions, confirm figures with your bank or a qualified adviser.