See exactly how your savings and investments grow over time ā with regular contributions, your choice of compounding, and a transparent year-by-year breakdown.
Your numbers
Results update automatically as you type.
Results
Final balance
$0.00
After 20 years of investing.
Starting principal
$0.00
Total contributions
$0.00
Total interest earned
$0.00
Growth over time
Stacked by source, year by year.
PrincipalContributionsInterest
Year-by-year breakdown
Year
Starting balance
Contributions
Interest
Ending balance
The formula behind the numbers
For transparency, here's the math this tool uses.
Principal growth:A = P Ć (1 + r/n)nĀ·tRecurring contributions (future value of an annuity):FV = PMT Ć [ ((1 + r/n)nĀ·t ā 1) Ć· (r/n) ]
P = principal Ā· PMT = contribution per period Ā· r = annual rate (decimal) Ā· n = compounds per year Ā· t = years.
This calculator simulates each compounding period and deposits contributions on their schedule, so any mix of contribution and compounding frequency stays exact.
What is compound interest?
Compound interest is the interest you earn on your interest. Unlike simple interest ā which only ever pays you on your original deposit ā compound interest reinvests every gain, so each new period earns a return on a slightly larger balance. Over years and decades, that snowball effect is what turns steady saving into real wealth.
Here's the intuition: put $10,000 into an account earning 7% a year. After year one you have $10,700. In year two you don't just earn 7% on your original $10,000 ā you earn it on the full $10,700, giving you $11,449. The extra $49 is interest earning interest. It looks tiny at first, but it accelerates. This is why Albert Einstein is often (if apocryphally) said to have called compound interest "the eighth wonder of the world."
Why time matters more than timing
Because compounding builds on itself, the single biggest lever is how long your money stays invested. A dollar invested at 25 has decades to multiply; the same dollar invested at 45 has far fewer compounding cycles. Starting early ā even with small amounts ā usually beats starting later with larger ones.
How this calculator works
This tool combines two well-known finance formulas and then runs a period-by-period simulation so the results stay accurate no matter how you mix your settings.
Your starting principal grows using the standard compound interest formula at whatever frequency you choose ā daily, monthly, quarterly, or annually.
Your regular contributions are treated as a series of deposits (an annuity). Each deposit is added on its schedule and then compounds for the rest of the term, just like real money flowing into a brokerage or retirement account.
Interest is simply your ending balance minus everything you put in (principal + total contributions). That's the number the chart and cards highlight in gold.
A few assumptions worth knowing
Contributions are added at the end of each period (an "ordinary annuity"), the conservative convention most calculators use.
The interest rate is assumed constant. Real markets fluctuate year to year ā use this for projection and planning, not as a guarantee.
Results don't account for taxes, fees, or inflation. Your real-world, after-tax, inflation-adjusted return will typically be lower.
Frequently asked questions
What's the difference between compound and simple interest?
Simple interest is calculated only on your original principal, so it grows in a straight line. Compound interest is calculated on your principal plus all previously earned interest, so it grows on a curve that gets steeper over time. The longer your money is invested, the bigger the gap between the two.
How does compounding frequency affect my returns?
More frequent compounding means interest is added to your balance more often, so it starts earning its own interest sooner. Daily compounding earns slightly more than annual compounding at the same rate ā but the difference is usually small. Going from 7% compounded annually to daily adds only a fraction of a percent to your effective yield. Time and contribution amount matter far more.
Should I contribute monthly or annually?
Contributing monthly puts your money to work sooner and spreads your investing across market ups and downs (a practice called dollar-cost averaging), so it generally edges out one big annual deposit. That said, the most important thing is to contribute consistently with whatever cadence you can actually stick to. Use the Monthly/Annually toggle above to compare the two for your own numbers.
Is 7% a realistic interest rate to assume?
Seven percent is a common planning figure for a diversified U.S. stock portfolio ā it roughly reflects the long-run historical average of the S&P 500 after inflation. High-yield savings accounts and CDs typically pay far less (often 1ā5%), while individual stocks can swing much higher or lower. Choose a rate that matches where your money actually sits, and remember past performance never guarantees future results.
Does this calculator account for taxes and inflation?
No. The results show pre-tax, nominal (non-inflation-adjusted) growth. Depending on your account type and situation, real-world returns may be reduced by taxes, fees, and inflation. To estimate "real" purchasing power, you can subtract roughly 2ā3% from your rate to approximate inflation.
Is my information saved or sent anywhere?
No. Every calculation runs entirely in your browser. Nothing you type is uploaded, stored, or shared ā refresh the page and it's gone.