Compound Interest Calculator
See how an initial amount plus steady monthly deposits grows over time, and how much of the final balance is pure compound growth rather than your own money.
Adjustable compounding frequency, optional inflation view, and a year-by-year breakdown
The amount you start with today.
Added at the end of each month.
The long-run U.S. stock market average is around 7% after inflation, 10% before.
How often interest is added to the balance. More frequent compounding grows slightly faster.
Set above 0% to also see your future balance in today's dollars.
Future value
$0
You Contributed
$0
your own deposits
Interest Earned
$0
compound growth
Growth Share
0%
Why it accelerates: early on, most of your balance is money you deposited. Over time, interest earns interest of its own, so the green growth band pulls away from your contributions. The longer the horizon, the more lopsided it gets.
View year-by-year breakdown
| Year | Contributions | Interest | Balance |
|---|
Your PDF has been downloaded.
Check your downloads folder for your compound interest report.
Contributions vs compound growth
The lower band is the money you put in. The upper band is interest. Watch growth overtake contributions as the years add up.
Projected values are estimates and are not guaranteed. Actual results will vary.
The basics
How compound interest works
Interest earns interest
With simple interest you earn only on your principal. With compounding, each period's gains are added to the balance and then earn gains of their own. That feedback loop is the whole engine.
Time is the biggest lever
Compounding is slow at first and steep later. The last ten years of a long horizon usually add more than the first twenty. Starting early beats contributing more later.
Contributions feed it
Every monthly deposit starts its own compounding clock. Steady contributions, even modest ones, often matter more than chasing a slightly higher rate.
Rate matters, exponentially
A few extra percentage points compound into a very different result over decades. But higher expected returns come with more risk, so the rate you assume should match the investments you actually hold.
Frequency helps a little
Compounding daily instead of annually nudges your effective rate up slightly. It is real, but small next to time, rate, and how much you contribute.
Inflation is the quiet drag
A big future number buys less than it appears. Viewing your balance in today's dollars keeps your goals grounded in real purchasing power.
Put it to work
Compounding in a retirement account
Compound interest is the reason tax-advantaged retirement accounts are so powerful. Inside a 401(k) or Roth IRA, your gains are not taxed each year, so the full balance keeps compounding instead of leaking to taxes along the way. That uninterrupted compounding, stretched over a working lifetime, is what turns steady contributions into a retirement-sized number.
The same math also shows why fees and early withdrawals hurt so much. A single percentage point of annual fees does not just cost you 1% once; it removes that money from every future round of compounding. Pulling money out early does the same thing in reverse, ending the compounding on whatever you withdraw.
Use this calculator to build intuition, then see it in a real account: the 401(k) and Roth IRA calculators apply the same compounding to actual contribution limits, employer matches, and tax treatment.
See it in context
Related calculators
401(k) Calculator →
The same compounding, applied to real contribution limits and your employer match.
Roth IRA Calculator →
See tax-free compounding: in a Roth IRA, the growth is never taxed.
Retirement Calculator →
Put compounding into a full retirement projection with a readiness score.
Inflation Calculator →
The flip side of growth: see how inflation erodes a dollar over the same years.
Traditional IRA Calculator →
Project an IRA with deductibility checks and tax-deferred compounding.
Early Retirement Calculator →
See whether decades of compounding can fund leaving work early.