Investment Calculator
Project what regular investing might build over time, and see the point at which growth starts contributing more to the balance than you do.
What this projects
Given a starting balance, a regular contribution, and a return assumption, this shows what the account could grow to — and, more usefully, how much of that comes from your contributions and how much from growth.
The split is the point. Everything here rests on an assumed return that will not hold steady in reality, so treat the projection as a way of comparing scenarios rather than a forecast of any particular number.
The crossover
Look at the yearly table and find the year where growth first exceeds what you contributed that year. Early on, almost the entire balance is money you put in. Growth is a rounding error against your own deposits.
Then it crosses over, and from that point the account starts doing more work than you do. Reaching the crossover is most of what long-term investing is; it is why the advice is always to start early rather than to contribute more.
How it is calculated
Your annual return is converted into a rate for each contribution period:
period rate = (1 + annual)1/n − 1
Then each period the balance grows at that rate and the contribution is added. Contributing at the start of a period rather than the end earns one extra period of growth on every payment — a small effect per period that adds up over decades, which is why it is a toggle rather than an assumption.
A worked example
Start with $15,000, add $600 a month for 25 years, assume 6.5% a year. You contribute $180,000 across the period on top of the initial $15,000, and the projection lands near $508,900.
About $313,900 of that is growth — more than the $195,000 you put in. But note where it comes from: the final five years add more than the first fifteen. The balance being large is what makes the returns large.
On choosing a return figure
This is the input that most affects the result and is least knowable. A few honest observations:
- Long-run broad stock market returns have historically been high single digits before inflation, but with severe variation and long stretches of poor performance.
- Deducting inflation gives a figure in today's purchasing power, which is usually the more meaningful basis for planning.
- Fees come straight off the return. A 1% annual fee against a 7% return removes roughly a seventh of your growth, compounded.
- Running the projection at a lower rate as well as your central one tells you how much the plan depends on optimism.
What this cannot capture
- Volatility. A steady annual return is a fiction. Real sequences vary, and the order of good and bad years genuinely changes outcomes, particularly near the end.
- Tax. Not deducted. Treatment differs sharply between taxable and tax-advantaged accounts.
- Fees. Not deducted. Subtract them from your return figure to approximate their effect.
- Inflation. Figures are nominal, so a projected balance decades out buys considerably less than the same amount today.
- Real behaviour. Contributions get paused, and money gets withdrawn. Neither is modelled.
Frequently asked questions
What return rate should I assume?
There is no correct answer, which is why the field is yours to set. Many people use a conservative single-digit figure and then check how the plan looks at a lower one.
If the plan only works at an optimistic rate, that is useful information in itself.
Does it matter whether I invest at the start or end of the month?
Slightly. Contributing at the start gives every payment one extra period of growth. Over a long horizon the difference is real but modest — the toggle in the form lets you see it on your own figures.
Contributing consistently matters far more than the day of the month.
Is this projection adjusted for inflation?
No. To think in today's purchasing power, subtract your inflation assumption from your return — using roughly 4% instead of 7% gives a real-terms view.
Should I invest a lump sum or spread it out?
This calculator can model either, but it cannot tell you which is wiser, because that depends on the return sequence and on how you would react to a fall shortly after investing.
It is a question worth discussing with a qualified adviser rather than settling with a projection.
Why does the balance grow so much faster in later years?
Because returns are earned on the balance, and the balance is largest at the end. A 6% return on $400,000 is $24,000 — more than four years of contributions at $600 a month. The same percentage applied to a bigger number is simply a bigger number.
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This calculator is provided for general educational and estimation purposes only. It does not constitute investment advice, and no return shown here is a prediction or a guarantee. Investments can fall as well as rise, and past performance does not indicate future results. Consider speaking to a qualified financial adviser before investing.