Free Investment Return Calculator Online

An investment return calculator projects what a portfolio could grow into when you're contributing money regularly, not just depositing it once and walking away. That's the scenario most people are actually in with a brokerage account, an index fund, or a retirement account outside of employer matching — an initial amount, followed by a recurring monthly addition, growing at some assumed rate of return over a stretch of years. This tool runs that specific combination and reports the final value, how much of it came from your own contributions versus market growth, and the overall percentage return.

How the Investment Return Calculator Works

Four values, entered one per line in the input pane:

• Line 1 — Initial investment, the amount you're starting with, e.g. 10000.
• Line 2 — Monthly contribution, how much you're adding every month going forward, e.g. 500.
• Line 3 — Expected annual return as a percentage, e.g. 7.
• Line 4 — Time horizon in years, e.g. 20.

With auto-convert left on, the projection recalculates about a third of a second after you stop typing, so testing a higher monthly contribution or a longer horizon and immediately seeing the new numbers is close to instant. The output breaks the result into future value, total amount contributed, total earnings (the gap between the two), and overall return percentage — all copyable with one click or downloadable as a plain text file. All of that math runs directly in your browser; the figures you type never leave your device to produce the projection. If you're building this calculation into a budgeting tool, a client-facing dashboard, or any automated workflow, the same math is exposed as an API endpoint documented at /docs, so you don't have to reimplement the formula from scratch.

Why Model Investment Growth This Way

Modeling a starting balance plus ongoing contributions is the realistic shape of most actual investing, which makes this calculation useful in a range of situations:

• Projecting a brokerage or index fund account. If you've already got money invested and you're adding to it monthly, this shows where that combination could land after a given number of years at an assumed average return.
• Comparing "start now" against "wait and start later." Running the same monthly contribution and return rate at two different time horizons makes the cost of delay concrete — a few years' difference in start date often changes the ending total by far more than people expect, purely because of how much longer the earlier dollars have to compound.
• Testing how much a larger monthly contribution actually matters. Increasing the monthly figure and comparing the new total earnings against the old shows the real payoff of that change in dollar terms, not just as an abstract percentage.
• Weighing a lump-sum windfall against spreading it out. Entering a windfall as the initial investment with a modest or zero monthly contribution shows one path; splitting the same total across the initial amount and monthly contributions over time shows another, letting you compare the two.
• Setting realistic expectations before opening an account. Seeing the actual gap between contributed and total value at different assumed rates is a fast way to get a feel for what a "moderate" versus "aggressive" return assumption actually does to a long-term number.
• Deciding how to split a raise between spending and investing. Adding the extra amount to the monthly contribution line and comparing the new future value against the old one shows exactly what routing that raise into an investment account would be worth by the end of the horizon, in dollars rather than in the abstract.

The Math Behind the Projection

The calculator treats your initial investment as a lump sum compounding monthly at the entered rate, and your monthly contribution as a separate ongoing series added to the growing balance every month. These are combined using the standard future-value-of-a-lump-sum formula for the initial amount and the future-value-of-an-annuity formula for the monthly contributions, added together for the total.

A worked example: $10,000 to start, $500 added every month, a 7% assumed annual return, over 20 years. The initial $10,000 alone grows to about $40,387.39 through compounding. The monthly $500 contributions, growing alongside it, add roughly $260,463.33 more. Combined, the projected future value comes out to about $300,850.72. Total contributions over the 20 years — the initial $10,000 plus 240 months of $500 — add up to $130,000. That means the difference between what was put in and what came out is about $170,850.72 in earnings, a return of roughly 131.4% on the amount actually contributed. The split matters: contributions make up less than half of the final total, with the rest coming entirely from assumed market growth compounding over two decades.

Stretch or shrink the time horizon with everything else held constant and the picture changes sharply. The same $10,000 start and $500 monthly contribution at 7% comes out to about $106,639.02 after 10 years — earnings of roughly $36,639.02 against $70,000 contributed, a much smaller earnings-to-contribution ratio than the 20-year figure. Extend the same scenario to 30 years instead and the total reaches about $691,150.47, with earnings of roughly $501,150.47 against $190,000 contributed — earnings now well over double the total contributed. The pattern is consistent: the earnings share of the total grows disproportionately the longer the horizon runs, which is the practical case for starting an investing habit as early as possible rather than waiting for a "better" moment to begin.

What that projection does and doesn't account for:

Assumption	Reality
Fixed annual return	Real markets move unevenly year to year — a single assumed average smooths over volatility that would actually be part of the ride
Fixed monthly contribution	The model assumes the same amount every single month for the entire horizon, with no gaps or increases
No taxes on gains	Capital gains, dividends, and account type (taxable vs. tax-advantaged) all affect what you'd actually keep — not reflected in the raw projection
No fees	Expense ratios, advisory fees, or trading costs would reduce the real-world result below this projection
No inflation adjustment	The future value is a nominal figure unless you treat the input rate as already inflation-adjusted

This is a projection built from assumptions you control, not a forecast of what any specific account will actually return — real markets don't hold a constant rate for 20 straight years, and no calculator can predict which years will run ahead of or behind the average.

Investment Return Calculator vs. Other Ways to Estimate This

A few alternative paths to the same kind of number:

• Your brokerage's built-in growth projection. Many platforms show a projected balance tied to your actual holdings and history, which can be more tailored to your specific account but usually locks you into that platform's assumptions rather than letting you freely test different rates and contribution levels.
• A spreadsheet with a combined FV formula. You can replicate this exact calculation in a spreadsheet by combining a lump-sum future value formula with an annuity future value formula, which is worthwhile if this projection is one piece of a larger financial model you're maintaining.
• Portfolio-tracking apps. These are excellent for monitoring what you actually have today, but most aren't built to answer "what if I contributed $200 more per month" hypotheticals the way a dedicated calculator does.
• This calculator. Four numbers in, a full breakdown of contributed vs. earned out, recalculated instantly whenever you change an assumption. Best suited for quickly testing scenarios rather than tracking an actual live account.

How Your Numbers Are Processed

The initial amount, monthly contribution, return rate, and time horizon you enter are processed entirely on your own device using JavaScript running in your browser. None of it is transmitted to a server as part of generating the projection, no account is created to store it, and nothing is retained once you leave the page.

Common Questions About Investment Return Projections

What return rate should I assume?

There's no single correct answer — it depends heavily on what you're actually invested in and your risk tolerance. Running the calculator at a few different rates (say, a conservative 4-5% and a more optimistic 8-9%) shows the realistic range of outcomes rather than anchoring on one number as if it were guaranteed.

Why is the total earnings figure so much larger than the total contributed figure?

Over long horizons, compounding on both the initial amount and every monthly contribution — not just the final balance — means earlier dollars have far more time to grow than later ones. In the worked example above, earnings exceeded total contributions specifically because a 20-year horizon gave compounding enough runway to outpace the raw dollars put in.

Does this calculator account for market downturns?

No — it applies one constant assumed rate across the entire time horizon, which is a simplification. Real portfolios experience both up and down years, and the sequence of those returns (especially near the end of the horizon) can meaningfully affect the actual outcome in ways a single average rate can't capture.

How does this differ from a compound interest calculation?

Compound interest growth applies to a single lump sum with no further additions. This calculator adds a second moving part — a recurring monthly contribution growing alongside the initial amount — which is a more realistic model for an ongoing investment account. For the simpler lump-sum-only case, the Compound Interest Calculator is the more direct tool.

Is this the same as a retirement projection?

It's closely related but not identical — this tool has no concept of a current age, a target retirement age, or a withdrawal-phase income estimate. If those age-based and withdrawal-focused details matter to your question, the Retirement Calculator is built specifically around that framing.

Can I model a decreasing monthly contribution over time?

Not directly — the calculator assumes one fixed monthly figure for the entire horizon. If your contribution plan changes significantly partway through (for example, increasing once a raise kicks in), running the calculator separately for each segment of time with the updated contribution and combining the results by hand gives a reasonable approximation.

Does a longer time horizon always make a bigger percentage difference than a bigger monthly contribution?

Not universally, but time tends to have an outsized effect because it compounds on everything already in the account, not just on the newest dollars added. Doubling a monthly contribution roughly doubles the contribution side of the total, but adding another decade to the horizon lets both the existing balance and every contribution already made keep compounding, which is why the 30-year example above shows earnings growing far faster than contributions did across that same stretch.

Related Tools

For a lump-sum-only projection without ongoing contributions, the Compound Interest Calculator covers that simpler case directly. If your growth projection needs to be tied to a specific age and retirement date with a withdrawal-phase income estimate, the Retirement Calculator is the better fit. To evaluate the return on a single completed or hypothetical investment rather than an ongoing contribution plan, the ROI Calculator handles that comparison directly. And if you're working backward from a dollar target instead of forward from a contribution plan, the Savings Goal Calculator solves for the time needed to get there.