Compound growth means you earn returns on your earlier returns. Enter a starting amount, a monthly addition, a yearly return and the number of years. The tool shows your ending value and how much of it is growth.
A fair warning
Real markets do not return the same amount every year. Use a modest rate and treat the result as an illustration, not a promise.
Read: the power of compound growth
Keep learning about compound growth
Reading is a start, practice makes it stick. Run the numbers in our investor tools, test yourself in Stock Jeopardy, or follow the start here guides to see what to read next after compound growth.
Further reading: Investor.gov from the U.S. SEC and the Canadian Securities Administrators investor education site offer free, independent guides for new investors.
The three things that drive compounding
Compound growth depends on the amount you put in, the rate of return, and time. Of the three, time is the one most people undervalue. The earlier money starts, the more years it has to earn returns on its own earlier returns.
A worked example with made up numbers
Say you start with $5,000, add $200 a month, and assume a steady 7% yearly return for 20 years. Using monthly compounding, the end value comes to roughly $124,000. You would have put in about $53,000 ($5,000 plus 240 payments of $200). That means about $71,000 came from growth. Other calculators may round slightly differently, so treat these as close estimates.
Now change one thing. Start 10 years later, keeping the same amounts and 7% return, with only 10 years to go. The result is roughly $44,700. You put in about $29,000 and growth supplied the rest. Half the time did not give half the result. It gave about a third. That is the power of the later years, when the base is large.
Why “steady 7%” is only a picture
Real markets do not deliver the same return each year. A stock fund might rise 20% one year and fall 15% the next. The order of those years matters, especially when you are putting in or taking out money. A calculator needs one smooth number to work, so its answer is an illustration, not a forecast. No one knows future returns, and the future can differ from the past.
It is wise to try a low case and a high case. Run the same plan at 4% and at 8% and see the range. If the low case still meets your goal, you have more room for surprises.
Mistakes to avoid
- Using an optimistic return because it makes the answer look nice.
- Forgetting fees and taxes, which reduce the return you actually keep.
- Stopping contributions after a drop. Steady saving through bad years is a big part of the story.
- Ignoring inflation. A future dollar buys less than a dollar today.
- Counting on one number. Use ranges.
Where to go from here
A quick mental shortcut helps. The rule of 72 says to divide 72 by the yearly return to estimate the years needed to double. At 6%, it is about 12 years. Use it to sanity check any calculator result.
If you want to see how regular monthly buys play out in a rising and falling market, try the dollar cost averaging calculator. And when you are ready to think about how the pieces fit together, our guide on how to build a stock portfolio is a good next read.
Everything here is education only, not advice, and the numbers are made up.
Small changes in the inputs, large changes in the result
Try changing one input at a time and write down what moves. Raising the monthly amount from $200 to $250 adds money in every year. Raising the return from 7% to 8% affects every dollar, including the growth that is already there. Adding five more years often changes the result more than either of the others. This kind of testing shows which lever you actually control. You cannot pick the market return, but you can pick how long you stay and how much you add.
Compounding works on costs too
Fees compound just like returns. A yearly cost of 1% taken from a 7% return leaves 6%. Over 20 years, that gap can mean tens of thousands of dollars in a plan like the one above. The same goes for borrowing. Interest on debt compounds against you, which is why paying off high interest debt is often a sound first step before investing. Whenever you use the calculator, try a run with a lower return to represent fees, and notice the gap. The full calculator list has more tools to test other what if questions.
Questions people ask about compound growth
Does compound growth work the same every year?
No. Real investments rise and fall from year to year. A calculator uses one steady rate so the idea is easy to see, but actual results are uneven. Some years may be negative. The steady rate is only an example, not a promise of what any investment will do.
Why does starting early matter so much?
Growth is earned on earlier growth, so extra years give the effect more time to build. A smaller amount held for a long time can end up close to a larger amount held for a short time. Time is one of the few things every investor can use, at no cost.
Do fees and taxes change the result?
Yes. Fees and taxes take a small share each year, and that share also stops growing. Over many years, even a small yearly cost can reduce the final number by a meaningful amount. It helps to enter a lower, more cautious rate when you try the calculator.
Can I rely on the calculator’s final number?
Treat it as a rough picture, not a forecast. The result depends entirely on the rate and time you type in. Try several rates, including low ones, to see a range of outcomes. Use the calculators to compare them.
Quick recap
Compound growth means earning returns on past returns. Time and consistency matter most. Real results vary, and costs reduce them. Use the calculator to build understanding, and try cautious numbers so the range of outcomes feels realistic rather than hopeful.
Education only, not investment advice. Numbers in examples are made up.
