Investment Calculator
Project investment growth from a lump sum plus monthly contributions
📈 Investment details
Last updated June 2026
Method: Projects future value as the sum of two standard formulas - growth of the initial lump sum, FV = PV × (1 + i)n, and the future value of monthly contributions, PMT × (((1 + i)n − 1) ÷ i). Returns compound monthly (i = annual rate ÷ 12).
Included: Initial investment, recurring monthly contributions, total contributions, total investment gains, and a year-by-year growth table.
Not included: Taxes, account or fund fees, inflation, variable year-to-year returns, and mid-year contribution timing. Results are nominal pre-tax estimates, not a guarantee of future returns.
Investment calculator: how your money grows
Suppose you start with $10,000, add $500 every month, and earn an average 7% per year for 20 years. You will have personally contributed $130,000 ($10,000 plus 240 monthly deposits of $500), but your projected balance is about $300,000. That extra ~$170,000 is pure compound growth - money your money earned. This investment calculator separates the two so you can see exactly how much comes from saving versus how much comes from compounding.
The formula behind the projection
The final balance is the sum of two future-value formulas - one for your starting lump sum and one for your stream of contributions:
FV = PV × (1 + i)n + PMT × (((1 + i)n − 1) ÷ i) Here PV is your initial investment, PMT is your monthly contribution, i is the monthly return (annual rate ÷ 12), and n is the number of months (years × 12). The first term grows your starting balance; the second is the future value of a monthly annuity. This calculator compounds monthly and adds each contribution at the end of the month.
Why time matters more than amount
Compounding rewards duration above all else. A dollar invested at 7% roughly doubles every decade, so money invested in your 20s can compound through several doublings before retirement, while the same dollar invested in your 50s gets only one. That is why two people who contribute the same total can end up with very different balances - the early starter simply gives compounding more cycles to work. Increase the "years" field in the calculator and watch the final balance rise far faster than the contributions do.
Nominal vs. real (inflation-adjusted) returns
The projection here is nominal - it does not subtract inflation or taxes. Historically the broad U.S. stock market has returned roughly 10% per year before inflation and about 7% after it. To approximate purchasing power in today's dollars, enter the lower "real" rate (around 7%) instead of the nominal one, or run the nominal figure through the Inflation Calculator to see what it would actually buy. Remember these are long-run averages; real markets are volatile, and a run of weak returns early on can change the outcome considerably.
Putting it to work
- Automate contributions: a steady monthly amount harnesses dollar-cost averaging and removes the temptation to time the market.
- Raise the rate of saving, not the rate of return: you control how much you contribute; you do not control the market.
- Mind fees: even a 1% annual fee can erase a large share of long-term gains - use low-cost funds.
- Reinvest earnings: compounding only works if dividends and gains stay invested rather than being withdrawn.
How to use this investment calculator
You only need four inputs to get a realistic projection. Work through the fields in order:
- Initial investment: enter the lump sum you already have to put in today. If you are starting from zero, leave it at $0 and let the monthly contributions do the work.
- Monthly contribution: type the amount you plan to add every month. This is the lever you control most directly, so it is worth testing a few values.
- Annual return rate: use a rate that matches your asset mix. A diversified stock-heavy portfolio might use 7%-10%; a conservative bond-heavy mix would use less.
- Years invested: set your time horizon - how long until you plan to use the money. Push this number up and down to see how powerfully time changes the result.
The projection updates instantly. Read the projected balance at the top, compare it against your total contributions to see how much is pure growth, then scroll the year-by-year table to watch the balance accelerate over time.
Who this calculator is for
This tool helps anyone who wants to turn a savings habit into a concrete future number. That includes:
- New investors deciding how much to set aside each month to hit a goal.
- Retirement savers sanity-checking whether their 401(k) or IRA contributions are on track.
- Parents projecting a college fund or a custodial account over 10-18 years.
- Goal savers working toward a house down payment, a sabbatical, or financial independence.
- Anyone curious about the difference between simply saving cash and investing it for compound growth.
A second worked example: starting from zero
Suppose you have nothing saved yet but commit to $300 per month at an average 8% return for 30 years. You would contribute $108,000 of your own money over those three decades, yet your projected balance is roughly $447,000. More than 75% of that final figure is compound growth rather than your deposits. Now shorten the horizon to 20 years with the same $300/month and 8%: you contribute $72,000 and end up with about $176,000. The extra ten years - and the compounding cycles they buy - more than double the result even though you only added $36,000 more in contributions. This is why the years field moves the final number far more than small changes to the monthly amount.
Key terms explained
- Present value (PV): the lump sum you invest today - your starting balance before any growth.
- Future value (FV): what that money is projected to be worth at the end of the period, after compounding.
- Compounding: earning returns on your previous returns, not just on your original deposit. It is what makes the curve bend upward over time.
- Contribution (PMT): the recurring amount you add each period - here, every month.
- Rate of return: the annual percentage your investments grow. This calculator divides it by 12 to apply monthly compounding.
- Dollar-cost averaging: investing a fixed amount on a schedule so you buy more shares when prices are low and fewer when they are high, smoothing out your average cost.
What changes the result the most
If you adjust the inputs and watch the projected balance move, a few factors dominate the outcome:
- Years invested: the single most powerful lever, because compounding is exponential - each additional year adds more than the one before.
- Rate of return: a few percentage points compound into a large gap over decades, but it is also the input you control least.
- Monthly contribution: the amount you reliably control; raising it steadily builds the base that compounding multiplies.
- Initial investment: a head start helps, but over long horizons consistent contributions usually matter more than the opening balance.
Limitations and assumptions
This calculator is a planning estimate, not a forecast. Keep these assumptions in mind:
- It applies a single constant return every month; real markets are volatile and the sequence of returns can change your actual result significantly.
- It reports a nominal, pre-tax balance. Taxes on dividends, interest, and capital gains - plus inflation - all reduce your real, spendable amount.
- It assumes 0% in fees. Subtract your fund's expense ratio from the return you enter to approximate the real after-fee growth.
- Contributions are added at the end of each month; contributing at the start of the month would grow slightly faster.
- It does not model changing contributions over time, such as annual raises or pauses during a job change.
How it compares to related calculators
This page answers "how big could my investment grow with regular contributions?" If your question is different, a sister tool fits better:
- For growth of a single lump sum without contributions, use the Compound Interest Calculator.
- To find what a fixed future amount is worth today, use the Future Value Calculator.
- To measure the percentage gain on an investment you already made, use the ROI Calculator.
- To plan income and withdrawals for your later years, use the Retirement Calculator.
- To set aside money toward a specific target by a deadline, use the Savings Goal Calculator.
- To see how rising prices erode your future balance, use the Inflation Calculator.
Where you hold the investment changes what you keep
This calculator projects the same nominal balance regardless of account type, but the account wrapper you choose has a large effect on your real, after-tax result. A dollar that compounds in a tax-advantaged retirement account is worth more than the same dollar in a regular taxable brokerage, because you defer or avoid tax on the gains along the way.
- Traditional 401(k) and IRA: contributions are typically pre-tax, the balance grows tax-deferred, and you pay ordinary income tax on withdrawals in retirement. Use the 401(k) Calculator to factor in an employer match, which is effectively a guaranteed return on top of market growth.
- Roth IRA and Roth 401(k): contributions are made with after-tax dollars, but qualified withdrawals - including all the compound growth - come out tax-free. For long horizons where gains dwarf contributions, that tax-free growth is especially valuable.
- Taxable brokerage: no contribution limits and full flexibility, but dividends and realized gains are taxed each year or when you sell. Long-term capital gains generally receive a lower rate than ordinary income.
A common order of priority is to capture any employer match first, then fund tax-advantaged accounts, and finally invest the rest in a taxable account. Because this calculator reports a pre-tax number, treat tax-advantaged accounts as getting you closer to the projected figure and taxable accounts as keeping somewhat less.
How to read the year-by-year growth table
Below the headline projection, the calculator builds a row for each year so you can watch the balance compound rather than just see the final number. Three things in that table are worth paying attention to:
- The widening gap: in the early years your balance tracks closely with what you have contributed, because there is little prior growth to compound. Further down the table the balance pulls away from total contributions as gains start earning gains of their own.
- The crossover year: on long horizons there is a point where cumulative gains overtake cumulative contributions - the year your money is doing more of the work than you are. Spotting that row is a vivid illustration of why early investing pays off.
- The acceleration at the end: the dollar increase in the final year is usually far larger than in the first, because the balance the return is applied to is so much bigger. This is the exponential curve in action, and it is why shaving even a few years off your timeline costs more than it appears.
If your goal is a specific dollar figure by a set date rather than open-ended growth, the Savings Goal Calculator works backward from the target to tell you the monthly amount you need, and the Compound Interest Calculator isolates the growth of a single lump sum.
Sources
- U.S. Securities and Exchange Commission (Investor.gov) - Compound Interest Calculator and the power of compounding.
- U.S. Securities and Exchange Commission (Investor.gov) - Investing basics: risk, return, and diversification.
- Consumer Financial Protection Bureau (CFPB) - Consumer tools for saving and investing.
- Internal Revenue Service (IRS) - Topic No. 409, Capital Gains and Losses.
⚠️ Common mistakes & edge cases
Using an unrealistically high return
Plugging in 15% or 20% makes the chart look great but sets false expectations. Long-run diversified portfolios have averaged closer to 7%-10%, and even that is not guaranteed. Plan with a conservative rate and treat upside as a bonus.
Ignoring inflation and taxes
A $300,000 nominal balance in 20 years buys far less than $300,000 today, and taxable accounts owe tax on gains. The result here is pre-tax and pre-inflation - mentally discount it, or use a real return to approximate purchasing power.
Assuming returns are smooth
The calculator applies one constant rate, but markets rise and fall. The order of returns matters: poor early years drag on the balance more than the average suggests. Use the projection as a planning guide, not a precise forecast.
Forgetting fees
This model assumes 0% in fees. A 1% expense ratio compounds against you exactly the way returns compound for you and can quietly consume tens of thousands of dollars over decades. Subtract your fund's expense ratio from the return you enter.
❓ Frequently asked questions
How does this investment calculator work?
It projects the future value of your investment using two parts: the growth of your starting lump sum and the growth of your recurring monthly contributions. The lump sum uses FV = PV x (1 + i)^n, and the contributions use the future-value-of-an-annuity formula PMT x (((1 + i)^n - 1) / i), where i is the monthly return (annual rate / 12) and n is the number of months (years x 12). The two results are added together for your projected balance.
What is a realistic rate of return to use?
A common long-run reference is the historical average annual return of the broad U.S. stock market, roughly 7% after inflation or about 10% before inflation, though returns vary widely year to year and the past does not guarantee the future. More conservative portfolios with bonds typically return less. Use a rate that matches your asset mix, and try a lower number to stress-test your plan.
What is the difference between my contributions and my gains?
Total contributions are the money you actually put in - your initial investment plus every monthly deposit. Gains are everything your balance earns on top of that through compounding. Over long periods, gains can grow to exceed the amount you contributed, which is the core benefit of investing early.
Does this calculator account for taxes and inflation?
No. The projection is a pre-tax, pre-inflation estimate of nominal balance. Taxes on dividends, interest and capital gains, account fees, and inflation will all reduce your real, spendable result. For a rough inflation-adjusted view, enter a lower 'real' return (for example 7% instead of 10%).
Why does starting earlier make such a big difference?
Compounding means your earnings generate their own earnings. The longer money stays invested, the more compounding cycles it goes through, so contributions made early have far more time to grow than identical contributions made later. Increasing the number of years in the calculator shows how steeply the final balance rises with time.
How is monthly compounding different from annual compounding?
With monthly compounding, returns are credited 12 times a year and each month's growth is included in the next month's base, so the effective annual yield is slightly higher than the stated rate. This calculator compounds monthly and assumes contributions are added at the end of each month.
Is the projected return guaranteed?
No. This is an estimate based on a single constant rate you choose. Real markets fluctuate, and a sequence of poor early returns can produce a very different outcome than a smooth average suggests. Treat the result as a planning guide, not a promise.
What inputs do I need to use this calculator?
Four numbers: your initial investment (the lump sum you have today, which can be $0), your monthly contribution, an expected annual return rate that matches your asset mix, and the number of years you plan to stay invested. The projected balance, total contributions, total gains, and a year-by-year table update instantly as you change any field.
How do fees affect my projected balance?
Fees compound against you the same way returns compound for you. A 1% annual fee behaves like a 1% lower return, which can quietly cost tens of thousands of dollars over several decades. This calculator assumes 0% in fees, so subtract your fund's expense ratio from the return you enter to approximate your real, after-fee growth.
Is it better to invest a lump sum or contribute monthly?
If you already have the cash, investing a lump sum gives your money the most time to compound and has historically come out ahead on average. Contributing monthly (dollar-cost averaging) is what most people actually do from a paycheck, and it smooths out your purchase price and removes the pressure of timing the market. This calculator lets you combine both - a starting lump sum plus ongoing monthly contributions.
Does the type of account I invest in change the result?
This calculator projects the same nominal balance regardless of account, but the account type changes how much you keep after tax. In a traditional 401(k) or IRA the balance grows tax-deferred and you pay tax on withdrawals; in a Roth account qualified withdrawals are tax-free; in a taxable brokerage account dividends and realized gains are taxed along the way. For long horizons, holding investments in a tax-advantaged account leaves you closer to the projected pre-tax figure than a taxable account does.
💡 Good to know
Time in the market beats timing the market
Because compounding is exponential, the years you stay invested usually matter more than picking the perfect entry point. A consistent contribution started early and left alone tends to outperform sporadic, larger deposits made later.
The number shown is before taxes and inflation
Your projected balance is a nominal, pre-tax figure. To approximate spending power in today's dollars, enter a lower "real" return (for example 7% instead of 10%) and remember that taxable accounts owe tax on gains.
Fees compound against you
A 1% annual fee works exactly like a 1% lower return - quietly draining tens of thousands of dollars over decades. Subtract your fund's expense ratio from the return you enter so the projection reflects what you actually keep.