Investing

Investment Calculator

Model where consistent investing leads. Enter a starting amount, a monthly contribution, and an expected return to project your portfolio's value over time — split between the money you put in and the growth the market added, with a year-by-year table of the journey.

Formula shown below · Tested against worked examplesHow we verify

Starting investment

Monthly contribution

Expected annual return

The S&P 500 has averaged ~10% nominal over the long run; diversified portfolios less. Fees subtract directly.

Years invested

Projected portfolio value

$548,915

Money you invested: $160,000
Market growth: $388,915
Share of final value from growth: 70.85%

Portfolio by year

Year	Value	Invested	Growth
1	$17,055	$16,000	$1,055
2	$24,695	$22,000	$2,695
3	$32,970	$28,000	$4,970
4	$41,932	$34,000	$7,932
5	$51,637	$40,000	$11,637
6	$62,148	$46,000	$16,148
7	$73,531	$52,000	$21,531
8	$85,859	$58,000	$27,859
9	$99,210	$64,000	$35,210
10	$113,669	$70,000	$43,669
11	$129,329	$76,000	$53,329
12	$146,288	$82,000	$64,288
13	$164,655	$88,000	$76,655
14	$184,546	$94,000	$90,546
15	$206,088	$100,000	$106,088
16	$229,419	$106,000	$123,419
17	$254,685	$112,000	$142,685
18	$282,049	$118,000	$164,049
19	$311,684	$124,000	$187,684
20	$343,778	$130,000	$213,778
21	$378,537	$136,000	$242,537
22	$416,180	$142,000	$274,180
23	$456,948	$148,000	$308,948
24	$501,099	$154,000	$347,099
25	$548,915	$160,000	$388,915

Compare scenariosTry three values of one input

Vary

Investment Calculator results for three values of Starting investment
Starting investment
Projected portfolio value	$541,575	$548,915+$7,340	$556,255+$14,680
Money you invested	$159,000	$160,000+$1,000	$161,000+$2,000
Market growth	$382,575	$388,915+$6,340	$395,255+$12,680
Share of final value from growth	70.64%	70.85%+0.21%	71.06%+0.42%

Every other input stays at the value you set above — currently $10,000 for starting investment. Differences are measured against the first column.

Saved scenariosSave this calculation

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Saved in this browser only — no account, and nothing is sent to us. Clearing your browser data deletes them.

How this calculator works

Growth compounds monthly at your expected return with contributions at month-end, in exact cents — a standard deterministic projection. Real portfolios experience volatility and sequence-of-returns risk that a single-rate model cannot show.

Results are pre-tax and pre-inflation. Long-horizon planning in today's dollars: use a real return (nominal minus ~3%).

Formula

FV = P(1+i)ⁿ + C × ((1+i)ⁿ − 1) ÷ i

Contributed = P + (C × n)
Growth      = FV − Contributed

FV: Projected value
P: Initial investment
C: Contribution per period
i: Expected return per period, as a decimal
n: Number of periods

The return is an assumption, not a forecast, and real markets deliver it unevenly. Splitting the result into what you contributed and what growth added is the honest way to read it: early on the balance is mostly your own money.

What this assumes

A constant annual return, compounded on schedule. Actual returns arrive unevenly, including falls of 30% or more.
No fund fees. A 1% expense ratio over thirty years can consume around a sixth of the final balance.
No tax on gains or dividends, which applies inside a retirement account but not in a taxable brokerage.

What changes this number

Time invested: The largest input. The final years contribute disproportionately, and they are only available to someone who started earlier.
Fees: The one input you fully control and can check in advance. It is deducted from fund assets rather than billed, so nothing prompts you to notice it.
Assumed return: 7% after inflation is a long-run historical average, not a promise. Plan at a rate you would still accept if it disappointed.

A worked example

Take the index fund starter: $500/mo for 30 years scenario. These figures are produced by the calculator above, not written alongside it, so they always match what the tool returns.

What you enter

Starting investment: $1,000
Monthly contribution: $500
Years invested: 30 years

What it returns

Projected portfolio value: $756,116
Money you invested: $181,000
Market growth: $575,116
Share of final value from growth: 76.06%

Sources

This calculator uses no external data — the result follows entirely from the formula above and the values you enter, so there is nothing to cite beyond the arithmetic.

Calculator last reviewed August 8, 2026. How we verify

Try an example

Index fund starter: $500/mo for 30 years Windfall: $100k lump sum, no additions Fee check: same plan at 7%

Frequently asked questions

What return should I expect from investing?

US large-cap stocks have averaged about 10% a year nominal (roughly 7% after inflation) over the past century — with brutal individual years on both sides. Diversified stock/bond portfolios land lower. Model 6–8%, subtract your fund fees, and treat anything above as upside.

Is a smooth average return realistic?

No single year is average — markets lurch (+30% one year, −20% another) and only average out over decades. A constant-return projection is the right planning tool for long horizons, but expect the real path to be jagged. That's the price of the returns.

What is dollar-cost averaging?

Investing a fixed amount on a schedule regardless of prices — exactly what the monthly contribution here models. You automatically buy more shares when prices are low and fewer when high, and more importantly, you remove timing decisions that most investors get wrong.

How much do fees matter?

Enormously at scale: a 1% annual fee on an 8% return doesn't cost 1% — it compounds. Over 30 years it can consume a quarter of the final balance. Re-run this calculator at 7% vs 8% to see your own number; broad index funds under 0.1% make the problem nearly vanish.

Should I invest a lump sum or spread it out?

Historically, investing a windfall immediately beats spreading it out about two-thirds of the time (markets rise more often than they fall). Spreading over 6–12 months trades a bit of expected return for regret protection — a reasonable, human choice.

What will $25,000 grow to in 20 years?

Starting with $25,000 and adding $500 a month at a 7% return, about $361,432. You would have invested $145,000 of that, with $216,432 coming from growth — just under 60% of the final value. Returns are not guaranteed and real markets deliver this unevenly.

This calculator helps answer

Should I pay off debt or invest?

Compare a guaranteed return you cannot lose against an expected one you might. The answer is clear at both extremes and genuinely close in the middle.