Compound Interest Calculator

Calculate compound interest and project savings growth with regular contributions and any compounding frequency.

100% Browser-Based • Local Processing
% a year
yr

A projection at a fixed rate, not a forecast. Real returns vary, and tax, fees and inflation are not deducted. Not financial advice.

Balance after 10 years

54,713.58

You put in 34,000.00
Interest earned 20,713.58
Interest share 37.9%
Formula and working

The formula

A = P(1 + r/n)^(nt) + PMT × ((1 + i)^m − 1) ÷ i

Your numbers

Waiting for your numbers.

Year-by-year growth
YearDepositsInterestBalance
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Privacy Focused

🔒 Local Processing. Your numbers never leave your device.

Instant Results

🌐 Fully Client-Side. Runs instantly in your browser.

No Signup

⚡ No accounts. No API keys. Just open and use.

Browser Based

🚀 No installs, no sign-ups, no server round-trip.

Overview

What is a Compound Interest Calculator?

A Compound Interest Calculator projects how savings or an investment grow over time when interest earns interest. From a starting amount, an annual rate, a term, and how often interest compounds — plus any regular contributions — it shows the final balance, total contributions, and total interest earned, with the formula and a year-by-year breakdown. It runs in your browser.

Compound interest is interest earned on both your original money and the interest it has already earned — the effect that makes long-term saving and investing powerful. Small differences in rate, time, and how often it compounds add up dramatically.

This calculator projects that growth, including regular deposits, and shows the year-by-year path. It runs entirely in your browser, so your figures stay private.

Guide

How to calculate compound interest

Step 1: Enter your starting amount, the annual interest rate, and the number of years

Enter your starting amount, the annual interest rate, and the number of years.

Step 2: Choose how often interest compounds, and add any regular contribution

Choose how often interest compounds, and add any regular contribution.

Step 3: Read the final balance, total interest earned, and the year-by-year growth

Read the final balance, total interest earned, and the year-by-year growth.

Screens

Compound Interest Calculator in action

Compound Interest Calculator projecting savings growth in the browser.
Growth result
Year-by-year compound growth with contributions.
Year-by-year chart
Calculating compound interest on a phone, no app installed.
Mobile (stacked)
Details

How compounding works — and why time matters most

Compound interest grows by the formula A = P(1 + r/n)^(nt), where P is the principal, r is the annual rate (as a decimal), n is the number of times it compounds per year, and t is the number of years; with regular contributions, each deposit is added and then compounds for its remaining time, which the calculator sums for you. Two levers stand out. Compounding frequency: more frequent compounding (monthly vs annually) earns a little more, because interest starts earning interest sooner. But time is the dominant factor — because growth is exponential, money left longer doesn't just add up, it accelerates, which is why starting early beats contributing more later. The year-by-year table makes this visible: the annual gains get bigger over time even with the same rate. Be clear about the assumptions: the projection uses a constant rate and steady contributions, whereas real investment returns fluctuate and can be negative in some years; it also ignores taxes and inflation unless you lower the rate to a 'real' return to account for them. So treat it as an illustration of the mechanics, not a prediction, and not financial advice. Everything computes locally in your browser. For interest without compounding, use the Simple Interest Calculator; for a target, the Savings Goal Calculator.

Support

Frequently Asked Questions

How does compound interest work?

You earn interest on your principal and on the interest already added, so your balance grows faster over time. The formula is A = P(1 + r/n)^(nt): principal P, annual rate r, compounds per year n, and years t. Because gains build on previous gains, growth is exponential rather than linear.

What's the difference between compound and simple interest?

Simple interest is calculated only on the original principal (interest = P × r × t), so it grows in a straight line. Compound interest is calculated on the principal plus accumulated interest, so it grows faster and faster. Over long periods the difference is large — compounding is why investments can grow so much.

Does compounding frequency matter?

Yes, a bit. Compounding more often — monthly or daily versus annually — earns slightly more, because interest begins earning interest sooner. The effect is real but modest compared with the rate and, especially, the time invested. The calculator lets you set the frequency to see the difference.

Why does starting early matter so much?

Because compound growth is exponential, the longest-invested money produces the biggest gains — the later years grow far more than the early ones at the same rate. Starting earlier gives your money more time to compound, often outweighing larger contributions made later. The year-by-year table shows the gains accelerating.

Can I include regular contributions?

Yes. Add a regular deposit (monthly, yearly, etc.) and the calculator compounds each contribution for its remaining time, then sums everything. This models real saving — a starting amount plus ongoing deposits — and shows how regular investing combines with compounding to build the final balance.

Is this a guaranteed projection of my returns?

No. It assumes a constant rate and steady contributions, but real investment returns vary year to year and can be negative, and the tool ignores taxes and inflation unless you reduce the rate to a 'real' return. Use it to understand the mechanics and compare scenarios, not as a prediction — and it isn't financial advice.

Is it free, and do I need to sign up?

Yes, it's completely free with no account, no trial, and no limit on how many times you use it. It runs entirely in your browser, so there's no sign-in wall — just open the page and calculate.

Is my data private?

Yes. Everything is calculated in your browser — the numbers you enter are never sent to a server, and nothing is stored once you close the tab. That keeps any personal figures (salary, loan, health) on your own device.

Does it work on mobile?

Yes. It runs in your phone's browser with nothing to install, so you can calculate on Android or iOS. The layout adapts to small screens, so entering numbers and reading the result is easy on the go.

Does it work offline?

Once the page has loaded, the calculation runs entirely on your device, so it keeps working without a connection. You only need to be online to open the page the first time — which is also why nothing you enter is uploaded.

Can I copy or share the result?

Yes. You can copy the result to your clipboard with one click, and many results can be shared. Because everything is calculated locally, copying is instant with no upload step.

How accurate is it, and is this professional advice?

The math is accurate for the inputs you give, and the formula is shown so you can verify it. But results are estimates for general use, not professional advice — finance calculators use simplified assumptions and ignore fees and rate changes, and health calculators are general estimates, not medical advice. For important decisions, consult a qualified professional.

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