Compound Interest Calculator
This calculator projects how an investment grows when interest compounds — earning returns not just on what you put in, but on the returns already earned. Enter a starting balance, a regular contribution, a time horizon, and an expected annual return, and the Future Value, the growth chart, and the contribution-vs-interest breakdown all update instantly as you type, right in this browser tab.
How This Compound Interest Calculator Works
Four numbers drive the projection: Initial Investment (what you start with), Regular Contribution (what you add on an ongoing basis), Years to Grow, and Annual Return Rate. Each keystroke re-runs the full period-by-period calculation and updates the Future Value hero, so there's nothing to submit and nothing to wait for. Below the headline number, Total Contributions shows exactly how much of the final balance is money you put in, and Total Interest Earned isolates the pure growth on top of that — the part compounding actually did for you.
Why Compounding Frequency Changes Your Results (Daily vs. Monthly vs. Yearly)
Tap Advanced to reveal Compounding Frequency — how often earned interest gets folded into your balance so it starts earning interest of its own. Most calculators quietly assume one frequency and never say which, so the same numbers can produce different answers on different sites. This one lets you switch between Daily, Monthly, and Yearly and watch the Future Value move, so you can match whatever your actual account statement says instead of guessing.
A higher compounding frequency produces a slightly larger Future Value at the same stated annual rate, because interest starts compounding on itself sooner. The gap is small over a few years at a modest rate; it becomes more noticeable over decades or at a higher rate — the calculator does the exact math for your own numbers rather than a rule of thumb.
Adding Regular Contributions to Your Growth
Contribution Frequency — also under Advanced — is separate from Compounding Frequency, because how often you add money and how often interest compounds are two different real-world facts. Set Regular Contribution to whatever you actually add (say, $500 a month), pick how often you add it, and the calculator spreads that contribution across every compounding period so the total added over a year always matches what you entered — even if your compounding and contribution frequencies don't line up on the same calendar.
Adjusting for Inflation: Real vs. Nominal Value
The headline Future Value is a nominal figure — tomorrow's dollars, not today's buying power. Enter an Inflation Rate under Advanced and the calculator adds a second figure, In today's dollars, dividing the Future Value by your inflation rate compounded over the same number of years. That's the real value — what your projected balance would actually be worth if prices rise at the rate you specified.
Reading the Growth Chart
The stacked area chart shows where your balance comes from at every point along the way: the bottom band is your unchanging Initial Investment, the middle band is cumulative Contributions added over time, and the top band is Interest — the pure compounding growth stacked on top of both. As the years pass, the widening green interest band is compounding visibly taking over as the largest driver of the total, which is the whole point of starting early.
Frequently Asked Questions
Is compounded monthly or annually better?
Monthly compounding produces a slightly higher balance than annual compounding at the same stated annual rate, because interest starts earning its own interest sooner — twelve times a year instead of once. The difference is small at low rates and short timeframes but grows over decades, which is exactly why this calculator lets you switch Compounding Frequency and watch the Future Value change instead of taking one fixed assumption on faith.
What's the difference between compounded monthly and annually?
Annual compounding applies your interest rate once per year to the whole balance. Monthly compounding splits that same annual rate into twelve smaller applications, each one calculated on a balance that already includes last month's interest. Over a long horizon that extra compounding adds up — enter the same numbers here with Compounding Frequency set to Yearly, then Monthly, to see the exact dollar gap for your own inputs.
Does compounding frequency actually matter?
Yes, though how much depends on your rate and timeframe. At a modest rate over a few years the gap between daily and yearly compounding is small; at a higher rate over several decades it can add up to a meaningfully larger Future Value. It's also the single biggest reason two "compound interest calculators" give two different answers for the same numbers — most hard-code one frequency and never tell you which.
What is compounding frequency?
Compounding frequency is how often earned interest gets added to your balance so it starts earning interest of its own — daily, monthly, or yearly are the common options. A higher frequency means interest is credited more often, so each new bit of interest has more time left in the period to grow, which is why daily compounding edges out monthly, and monthly edges out yearly, at the same stated rate.
How often does a savings account's interest compound?
It varies by bank and account type, but daily and monthly compounding are the two most common arrangements for savings accounts, with the interest typically paid out — credited to your visible balance — once a month even when it compounds daily internally. Check your specific account's disclosure for its exact compounding frequency, then plug that setting into this calculator to project your own balance.
How do you calculate compound return on an investment?
Compound return applies your rate of return to the whole balance each period, including any return already earned in prior periods, rather than only ever applying it to your original amount. This calculator does that period-by-period math for you — enter your starting balance, expected annual return, and time horizon, and it runs the full compounding calculation instantly, adding any regular contributions along the way.
How often do banks compound interest?
Most banks compound savings and money-market interest either daily or monthly, while some certificates of deposit compound quarterly or even annually — there's no single industry standard. The compounding frequency is usually stated in your account's terms or truth-in-savings disclosure. Once you know it, set the same option here to see how it plays out over your actual timeframe.
