What is a compound interest calculator for investing?

It projects how an investment grows when returns earn returns — plus optional regular contributions. You set starting balance, contribution amount, expected annual return, compounding frequency, and years to see future value, growth share, and milestones.

How does compound growth work?

Compounding means gains are reinvested, so the next period earns return on a larger base. Over decades, contributions and compounding usually matter more than picking a single “winning” stock.

What return rate should I use?

Long-term U.S. stock market averages are often cited around 7–10% before or after inflation depending on the source. Use a conservative rate (e.g. 6–8%) for planning, not a best-case fantasy. Past performance isn’t a guarantee.

Should I adjust for inflation?

Yes for long horizons. Toggle inflation-adjusted value to see approximate purchasing power in today’s dollars. A large future balance can buy less than the same number today.

What do the “what if” comparisons show?

They estimate how much ending value changes if you contribute $100 more each period, earn 1% higher returns, or invest for 5 fewer years — so you can see which lever matters most for your plan.

Monthly vs annual compounding — does it matter?

More frequent compounding helps slightly when rates are fixed. For stock investors, “compounding” usually means staying invested and reinvesting dividends more than literal bank compounding schedules.

Is this compound growth calculator free?

Yes. No signup. Inputs save in your browser. Pair it with our DCA, retirement, inflation, and dividend tools for contribution habits and nest-egg planning.

All tools

Compound Growth Projector

Free compound interest calculator for investing. Project future value with contributions, inflation toggle, milestones, and what-if scenarios. No signup.

Project ending balance with contributions, return rate, and time — plus inflation view, $100k–$1M milestones, and what-if levers (save more vs earn more vs stay longer). Chart and year table included.

Time + contributions usually beat chasing a perfect return.

Project ending balance under your assumptions. Toggle inflation for purchasing-power view. Inputs save in your browser.

Projected value · 30 years

$799,858.37

of which $614,858.37 is growth (76.9%)

You put in

$185,000.00

Markets (growth)

$614,858.37

Growth share

76.9%

23.1% contributions

Grey = contributions · Green = compounded growth

Your plan

Currency

Initial investment ($)

Contribution ($)

Frequency

Expected annual return (%)

Planning tip: 6–8% is more conservative than a best-case fantasy.

Years

Show inflation-adjusted value

Growth chart

What if…

+$100 more per contribution+$149,035.94

+1% higher annual return+$189,166.25

Stop 5 years earlier-$287,644.30

Often “save a bit more” or “start/stay longer” beats hunting an extra percent of return.

Milestones

$100,000.00Year 10
$250,000.00Year 18
$500,000.00Year 25

Year-by-year

Expand for contributed vs growth each year — useful for screenshots and planning conversations.

What is a compound growth calculator?

A compound growth calculator (compound interest calculator for investing) estimates how money grows when returns are reinvested and optional contributions keep adding fuel. Instead of guessing “I’ll be rich someday,” you see a projected balance under clear assumptions — starting capital, contribution schedule, return rate, and time — plus how much of the ending pile is growth vs money you actually deposited.

Why compounding matters more than perfect timing

Time in the market beats timing the market for most long-term investors. A modest monthly contribution invested for 20–30 years can outgrow a larger lump sum started late. This projector makes that visible: tweak contribution size vs return rate and see which lever moves the ending balance more. The built-in what-ifs (+$100/period, +1% return, −5 years) make the trade-offs obvious. Deeper explainer: compound interest for investing.

How to use this free compound interest calculator

Enter starting balance (what you have invested today).
Add a contribution amount and how often you’ll invest (monthly is common).
Pick a realistic expected annual return — try the 6–8% presets for planning.
Choose years; optionally toggle inflation to see purchasing power.
Check milestones and what-if rows — then raise contributions before chasing risk.

Planning regular buys? Cross-check with our dollar cost averaging calculator. Nest-egg / FIRE math? Use the retirement calculator. Measuring past results? Try the investment return calculator.

Realistic assumptions beat optimistic ones

Fees and taxes: Lower your assumed return by 0.5–1%+ if you ignore costs in the model.
Inflation: Use the inflation toggle so a $500k future balance isn’t mistaken for today’s $500k. Pair with the inflation calculator for one-off purchasing-power checks.
Sequence risk: Markets don’t return a flat 8% every year; the calculator shows a smoothed path, not a guarantee.
Dividends: Model dividend reinvestment with our dividend & DRIP calculator.

Example: small contributions, long runway

$5,000 start + $300–$500/month at 7–8% for 25–30 years is a common “wow” scenario — most of the ending value usually comes from growth on reinvested gains and contributions, not from the initial lump alone. Run your own numbers above; then ask whether you can raise the contribution or stay invested longer before chasing a higher (riskier) return assumption.

Frequently asked questions

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Explore more free calculators and simulators on Swift Penguin: stock market simulator, stock screener, market heatmap, economic calendar, earnings calendar, compare stocks, stock watchlist, dividend calendar, live stock lookup, position size calculator, risk reward calculator, dividend & DRIP calculator, options profit calculator, portfolio tracker, dollar cost averaging calculator, average cost calculator, stock profit calculator, investment return calculator, capital gains tax calculator, retirement & FIRE calculator, inflation calculator, stop-loss calculator, Trading 212 portfolio charts, crypto prices & charts, crypto markets, crypto profit calculator, crypto DCA calculator, crypto position size, and crypto converter. Browse all free stock trading tools.

Projections are hypothetical and educational only — not financial advice. Actual results vary with markets, fees, taxes, and behavior.

Related guides

Basics7 min read

The Power of Compound Interest in Investing

Why starting early beats perfect timing — and how boring monthly contributions build serious wealth.

See why time beats timing, walk through a 30-year contribution example, and learn the habits (reinvest, stay consistent) that make compounding actually show up in your account.

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