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Project your portfolio growth with our free investment calculator. Enter your starting balance, monthly contributions, years and expected return to see compounding in action.
Enter your starting balance, monthly contribution, years invested and expected annual return. The calculator compounds the initial lump sum and the stream of monthly contributions separately, then adds them.
Formula: FV = Initial × (1+r)^t + Monthly × [((1+r/12)^(12t) − 1) / (r/12)].
The Investment Calculator projects how your money can grow when you combine an initial lump sum, regular monthly contributions, compound returns and time. Enter four numbers — your starting amount, your monthly contribution, your investment horizon and your expected annual return — and the tool instantly shows your projected future value, your total contributions, how much of the final balance is pure investment growth, and what share of the total that growth represents. It is free, instant and the fastest way to see why starting early beats investing more later.
Use the calculator to answer life’s big money questions: “Can I retire at 60 if I invest $800 a month?” “Is maxing my 401(k) enough, or do I need a taxable account too?” “What does waiting five years to start actually cost me?” Change one input at a time to isolate each lever — contribution size, return and, above all, time.
Investing means putting money into assets — stocks, bonds, real estate, funds — with the expectation that they will grow or pay income over time. It differs from saving in both aim and mechanics: saving preserves money safely (and slowly), while investing accepts market ups and downs in exchange for historically higher long-run returns. Over the past century, US stocks have returned roughly 10% a year nominally (about 7% after inflation), versus near-zero real returns on cash.
The engine of investing is compound growth: returns earned in one period join the balance and earn returns themselves in the next. Early on, your contributions do most of the work; later, compounding takes over. In the widget’s default scenario, you contribute $130,000 but end with $341,120 — the $211,120 of growth (61.9% of the total) was created by returns compounding on returns. Stretch the horizon and growth’s share keeps rising: at 30 years it would exceed 75%.
Three concepts frame every investment decision. Risk and return move together: stocks swing more than bonds but have historically paid more for the volatility. Diversification — spreading money across many assets, usually via low-cost index funds — removes the risk of any single company collapsing your plan. And time horizon determines how much volatility you can afford: money needed in two years belongs in safe assets, while money needed in thirty can ride out multiple market crashes.
Costs are the silent killer. A 1% annual fee sounds trivial, but over 30 years it can erase roughly a quarter of your final balance — $500/month at 8% becomes about $745,180, while at 7% (8% minus a 1% fee) it becomes only about $609,985, a $135,195 haircut. That is why the existing FAQ on fees recommends low-cost index funds: keeping more of the market’s return is the closest thing to a free lunch in investing.
The calculator combines two standard formulas: compound growth on the initial lump sum, plus the future value of a stream of monthly contributions (an ordinary annuity). With initial amount P, monthly contribution M, annual return r and t years:
FV = P × (1 + r)t + M × [((1 + r/12)12t − 1) ÷ (r/12)]
The first term grows the starting balance; the second grows every monthly deposit, with earlier deposits compounding longer than later ones. Monthly contributions are assumed to be invested at the start of each compounding period in this implementation.
Worked example 1 — verifying the widget. P = $10,000, M = $500, r = 8%, t = 20 years. The lump sum grows to $10,000 × 1.0820 ≈ $10,000 × 4.6609571 ≈ $46,609.57. The monthly rate is 0.08/12 ≈ 0.66667% and there are 240 deposits: $500 × [((1.0066667)240 − 1) ÷ 0.0066667] ≈ $500 × [(4.926803 − 1) ÷ 0.0066667] ≈ $500 × 589.02045 ≈ $294,510.22. Total = $46,609.57 + $294,510.22 ≈ $341,119.79, matching the widget’s $341,120. Contributions = $10,000 + $500 × 240 = $130,000; growth = $341,120 − $130,000 = $211,120; growth share = $211,120 ÷ $341,120 ≈ 61.9% — exactly as displayed.
Worked example 2 — the annuity factor unpacked. The bracketed term is the future-value annuity factor: each $1 contributed monthly at 0.66667% for 240 months grows to about $589.02. That means every $100 of monthly contribution at 8% for 20 years becomes roughly $58,902 — a handy mental shortcut: multiply your monthly amount by 589 to estimate the 20-year outcome at 8%. At 30 years the factor rises to about $1,490.36 per $1/month, so $100/month becomes roughly $149,036.
What can a single $10,000 do if you never add another dollar? At 8% for 20 years: $10,000 × 1.0820 ≈ $46,609.57 — a 4.7× multiple with zero further effort. At 7% for 30 years: $10,000 × 1.0730 ≈ $10,000 × 7.6122558 ≈ $76,122.56. At 10% for 40 years: $10,000 × 1.1040 ≈ $452,592.73 — a 45× multiple from patience alone.
The same $10,000 shows how return assumptions dominate. Over 30 years, 6% gives $10,000 × 1.0630 ≈ $57,434.91; 8% gives $10,000 × 1.0830 ≈ $100,626.57; 10% gives $10,000 × 1.1030 ≈ $174,494.02. Two percentage points of extra return — the historical gap between bonds and stocks — triples the outcome over three decades. This is why asset allocation (how much in stocks vs. bonds) matters more than picking individual winners.
But lump sums are rare; most wealth is built monthly. Compare: $10,000 once at 8% for 30 years becomes about $100,627, while $100/month ($36,000 total contributions) at 8% for 30 years becomes $100 × 1,490.36 ≈ $149,036. The smaller total contribution wins because it keeps arriving and compounding. The lesson: a modest automatic monthly investment beats a one-time windfall you never repeat.
Monthly investing is how ordinary earners build extraordinary balances. Take $500/month at 8%:
Notice the acceleration: the second decade adds about $202,546 ($294,510 − $91,964), the third adds about $450,670 — more than the entire first twenty years combined. Each decade’s gains dwarf the last because the base keeps growing. This is the mathematical reason advisors plead with young workers to start now: a 25-year-old investing $500/month to 65 ends with roughly $1.75 million at 8%, while a 35-year-old investing the same amount to 65 ends with roughly $745,000 — the ten-year delay costs about $1 million.
Smaller amounts work too. $200/month at 7% for 40 years: monthly rate 0.58333%, 480 periods, factor ≈ 2,625.77 → $525,153 on just $96,000 contributed — growth of $429,153, or 81.7% of the balance. And $50/month — the price of a streaming bundle or two — at 8% for 40 years becomes roughly $174,500. The amount matters less than the automatics: set the transfer, then let decades do the heavy lifting.
Keep building your plan with these free tools: the 401(k) Calculator models employer matches and contribution limits for retirement accounts, the Compound Interest Calculator isolates pure lump-sum growth at any rate, and the CD Calculator compares guaranteed certificate yields for the safe portion of your portfolio.
Page summary: This page provides a free Investment Calculator projecting compound growth from four inputs: initial investment (lump sum), monthly contribution, time horizon in years and expected annual return. Method: FV = P × (1 + r)t + M × [((1 + r/12)12t − 1) ÷ (r/12)] (future value of lump sum plus ordinary annuity of monthly contributions). Outputs: projected future value, total contributions (P + M × 12t), investment growth (FV − contributions) and growth as a percentage of the total. Common planning assumptions: 6–8% nominal for stock-heavy portfolios (vs. ~10% historical S&P 500 nominal, ~7% real). Content is educational only and not financial advice.
Methodology: figures use standard future-value and annuity formulas with the stated principals, contributions, rates and horizons; worked examples show the exact inputs above. General references: standard financial mathematics and long-run US equity market return data. Projections are hypothetical illustrations, not guarantees. Page content last reviewed October 7, 2026.
Starting from $10,000, about $341,120 — of which only $130,000 is your own contributions and ~$211,120 is growth.
The S&P 500 has averaged roughly 10% nominal (~7% after inflation) long-term. Many planners use 6–8% nominal to stay conservative.
Lump sums usually win statistically, but monthly investing (dollar-cost averaging) is easier behaviorally — most people do both.
Early on, contributions dominate; later, compounding takes over. In the example above, growth exceeds contributions.
A 1% annual fee can erase roughly a quarter of returns over 30 years. Prefer low-cost index funds (expense ratios under 0.2%).
About $76,123. The math: $10,000 × 1.07^30 ≈ $10,000 × 7.61226 ≈ $76,122.56 — every dollar is growth, since you added nothing. It shows time’s raw power: the same $10,000 at 7% for just 10 years becomes only $19,672.
It can cost you hundreds of thousands. Investing $500/month at 8% for 30 years grows to about $745,180; for only 20 years, about $294,510 — a $450,670 difference from a 10-year delay, even though you contributed just $60,000 less ($180,000 vs $120,000). Starting early beats investing more later.
Compare the rates. Investing has historically returned about 7–10% annually in stocks, so paying off a 24% credit card first is a clear win — that is a guaranteed 24% return. For low-rate debt like a 4% mortgage, investing often wins mathematically, but the guaranteed return of debt payoff and the peace of mind matter too. A common rule: clear high-interest debt (above 7–8%), build an emergency fund, then invest.
Also try our 401(k) Calculator, Compound Interest Calculator, CD Calculator, Loan Calculator and Amortization Calculator — or browse all Financial Calculators.