How this calculator works
The annual return and compounding frequency become an equivalent monthly rate. Each month the balance grows at that rate and your contribution is added. The breakdown separates your starting amount, contributions and investment growth.
Worked example
With the example values below: Ending balance, $300,851 (after 20 years). Change any number above to run your own.
What you enter
| Input | Example |
|---|---|
| Starting amount | $10,000 |
| Monthly contribution | $500 |
| Annual rate of return | 7% |
| Years | 20 yrs |
| Compounding | Monthly |
What drives investment growth
Three things decide how much an investment grows: how much you put in, the return it earns, and how long it compounds. Time is the most powerful. $10,000 plus $500 a month at 7% grows to about $183,000 in 15 years, $446,000 in 25 years and $962,000 in 35 years. Contributions are steady, but growth accelerates as the balance gets larger.
Starting five or ten years earlier usually matters more than finding a slightly higher return.
Choosing a realistic rate of return
US stocks have averaged roughly 10% a year before inflation over long periods, and bonds considerably less, but returns swing widely from year to year. A diversified stock-heavy portfolio is often modeled at 6% to 7% a year, and a balanced stock and bond mix at 4% to 6%. Using a lower rate gives a more cautious plan.
To see results in today's dollars, subtract expected inflation from your return. A 7% return with 3% inflation is about a 4% real return; the inflation calculator shows what future dollars will buy.
Fees and taxes reduce returns
A 1% annual fee can cost a quarter or more of your ending balance over 30 years, so low-cost index funds make a real difference; the mutual fund fee calculator shows the gap. Taxes matter too: investing through a 401(k) or Roth IRA lets growth compound without yearly tax drag.
Building a plan
For a full retirement picture with Social Security and withdrawals, use the retirement calculator.
- Keep an emergency fund in cash before investing money you might need soon.
- Capture any employer retirement match first.
- Choose a mix of stocks and bonds that fits your timeline; see the asset allocation calculator.
- Automate monthly contributions and raise them with each pay increase.
- Rebalance once or twice a year instead of reacting to headlines.
Frequently asked questions
How much will my investment be worth in 10 years?
It depends on your starting amount, contributions and return. $10,000 with $500 a month at 7% grows to about $105,000 in 10 years, of which $70,000 is your money and about $35,000 is growth.
What is a good rate of return on investments?
For long-term stock-heavy portfolios, 6% to 7% a year is a common planning assumption; balanced portfolios are often modeled at 4% to 6%. Past returns aren't guaranteed and real results vary widely year to year.
How much should I invest each month?
Many planners suggest saving 15% of gross income for retirement, including any employer match. Start with what you can, at least enough for the full match, and raise it with each raise.
Is it better to invest a lump sum or monthly?
Historically, investing a lump sum right away has beaten spreading it out about two-thirds of the time, because markets rise more often than they fall. Investing monthly reduces regret if prices fall soon after you start.
How does compound growth work in investing?
Returns are reinvested and earn returns of their own. Over decades, growth on past growth becomes the largest part of the balance, which is why starting early matters so much.
Grow what this calculator projects.
TruthSayer AI sends quantitative stock signals across valuations, earnings and dark-pool activity, each one traded in its own funded account first.
Estimates for planning only, not financial, tax or legal advice. Tax tools use 2026 federal figures (brackets, $16,100 / $32,200 standard deduction, $19,000 gift exclusion, $15M lifetime exemption). Rates shown as defaults are examples; replace them with quotes you actually receive.