Use this free compound growth and DCA calculator to see the year-by-year path of a starting balance plus regular contributions — including the year compounding starts adding more than you do.
How the compound and DCA calculator works
Enter a starting balance, a contribution per month or year, an expected annual return, and a horizon. The tool compounds the balance each period, adds the contribution at the end of that period, and reports the full schedule — not just the ending number. The headline figures are the final balance, everything you contributed, the growth on top, and the crossover year.
What the crossover year actually means
The crossover year is the first year in which cumulative growth exceeds everything you have put in. Before it, the balance is mostly your own savings; after it, the account earns more each year than you add. It is the clearest available answer to “when does compounding actually kick in?” — and it reframes patience as a mechanism rather than a slogan. It is also a shape, not a date: it assumes a constant return, and real sequences of returns move it around considerably.
A worked example
Start with $10,000, add $500 a month, assume a 7% annual return, and run it for 30 years. You contribute $190,000 in total. The ending balance is about $691,150, so roughly $501,150 — 72.5% of the final figure — is growth rather than contributions. The crossover lands in year 17: at year 16 cumulative growth is about $100,700 against $106,000 contributed, and by year 17 growth reaches roughly $115,800 against $112,000 contributed. From that point the account is doing more of the work than you are, and the last decade of the schedule adds more balance than the first two combined.
How to read the results
Read the growth share before the ending balance. A large final number driven almost entirely by contributions is a savings plan, not compounding; a large growth share is what you are actually trying to buy with time. The year-by-year table exists so you can see how late the curve bends — most of the gain sits in the final third of any long horizon, which is exactly why interrupting a plan early is so costly and why the last years matter most.
Common mistakes
The most common mistake is treating the crossover year as a forecast. It is the output of a constant-return model with no volatility, no fees, no taxes and no missed contributions. Change the return by a couple of points and the year moves substantially.
The second is comparing the ending balance in today’s dollars. Thirty years of inflation means the final figure buys far less than the same number would now — the growth is real, but the purchasing power is not what the headline suggests.
The third is assuming a bigger contribution is always the strongest lever. Over long horizons the return and the number of years usually move the crossover more than the contribution does. Over short horizons the reverse is true, and the contributions simply are the plan.
Where to go next
Compounding is only half the story — the other half is what those future dollars will actually buy, which is the subject of what inflation really is. If you want the contributions to happen without you thinking about them, how to automate your investing covers the setup. For the endpoint figure alone without the year-by-year path, use the compound growth calculator; to compare investing a lump sum against spreading it out, use the DCA vs. lump-sum calculator.
Frequently asked questions
When does compounding really start to matter?
At the crossover year, when annual growth begins to outpace your contributions. On the default inputs that is year 17 of 30.
Are contributions added before or after growth?
After, at the end of each period. That is the ordinary-annuity convention and the more conservative of the two choices.
Why is my crossover year so late?
Usually a short horizon or a modest return. Crossover is far more sensitive to years and rate than to the size of the contribution.
Educational tool, not financial advice. Past and modeled results do not guarantee future performance.
Where to invest: brokers with fractional shares
To act on what this tool shows you, you’ll need a brokerage account. These are established brokers we use that support fractional shares — buying a slice of a share by dollar amount, which makes dollar-cost averaging and diversifying with small amounts easy:
- Robinhood — commission-free investing with fractional shares from $1, and the only major broker offering a daily recurring-investment schedule. Recommended for most beginner-to-intermediate investors who want the simplest way to automate investing — see how to automate your investing for the full setup.
- Charles Schwab — fractional shares of most U.S.-listed stocks and ETFs from $1, commission-free online.
- Fidelity — “Stocks by the Slice” fractional investing from $1, with strong research and low-cost index funds.
Referral disclosure: the broker links above are referral links. If you open and fund an account through them we may receive a referral reward at no cost to you; it never affects our tools or conclusions. This is educational information, not investment advice — choose the broker that best fits your needs.