Personal Finance Score

Compound Interest Calculator

Compound interest is interest earned on both the money you put in and the interest from earlier periods. In the first years it is barely visible. After 20 to 30 years, the interest is usually larger than everything you put in.

The default example: start with $1,000, add $200 a month at 7% a year (an assumption you can change), compounded monthly. After 30 years the account holds about $252,000. You put in $73,000; the other $179,000 is interest.

The tool below redraws every year, marks the year interest passes what you add, and shows what starting 1, 5 or 10 years later costs. Everything runs on your phone; nothing is sent anywhere.

Free tool

Compound Interest Calculator

Enter an amount, a rate and a number of years. The tool redraws month by month how the money grows, and tells you the year your interest starts earning more than you do.

After 30 years you have
$252,111
Starting amount$1,000Money you add$72,000Interest earned$179,111
You put in$73,000
Interest earned$179,111
Interest share71%

Your numbers

$
$/mo
%
years
Compounds
Quick try
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Add money at
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How the money grows, year by year

Tap or hover the chart to see any year.

Milestones

    What does waiting cost?

    Delay:
    Start now
    Start 5 years later

    The formula inside
    For the starting amount: A = P × (1 + r/n)^(n×t)

    Monthly additions are added and compounded month by month, so the tool runs 12 steps a year instead of one formula.

    Year-by-year table
    YearAgeYou put in (total)Interest that yearInterest (total)Balance

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    Interest only grows when money sits in the right place

    Three places families often leave money idle:

    High-yield savings$10,000 at 0.01% earns $1 a year. At 3.20% it earns $320.→401(k) with employer matchContributing 3% instead of 6% on a $60K salary forfeits $900 a year of free employer money.→Trump Account for a child$1,000 from the government for children born 2025–2028, plus what you add, growing for 18 years.→

    Sources: IRS, 2026 limits: 401(k) $24,500 and IRA $7,500 (IR-2025-111). FDIC national average savings rate 0.38%, October 2026 (FRED SNDR). Ally Bank Savings 3.20% APY, checked 10/23/2026. The 7% in the default example is an assumption you can change, not a forecast or a promise. Updated 10/25/2026.

    This is education, not tax, legal or financial advice. Results are examples based on the numbers you enter, not guaranteed returns. Check your plan documents or a professional for your situation.

    Common questions

    Where does the 7% come from?

    It is an assumption so you have a starting point, not a forecast. Regular savings at large banks pay about 0.01% to 0.38% (the FDIC national average, October 2026). High-yield savings accounts pay about 3% to 4% as of October 2026. The U.S. stock market moves up and down each year and nobody guarantees a number. Try several rates to see the gap.

    Daily, monthly or yearly compounding: how big is the difference?

    Smaller than most people think. $10,000 at 5% a year for 10 years: yearly compounding gives $16,289, monthly $16,470, daily $16,487. The number of years and the rate are what decide the result.

    Does inflation eat the interest?

    Yes. Under “More options”, enter an inflation rate (for example 3%) to see the balance in today’s buying power. Money in a 0.01% account loses value every year.

    Which accounts is this for?

    401(k), IRA, Roth IRA, a child’s Trump Account, high-yield savings. Or run it in reverse: credit card debt at about 22% APR (Federal Reserve G.19) compounds the same way, against you.

    Read next: the 401(k) match, the first money to claim

    This is education, not tax, legal or financial advice. Check your plan documents or a tax professional for your situation.