Investment Calculator

Project how your money grows with compound returns and regular contributions — then see the realistic range of outcomes once you add market volatility.

Compound interest, contributions, optional inflation adjustment, and a Monte Carlo range.

See methodologyPlanning estimates only. Results depend on your inputs, tax status, and assumptions.

Compound growthRegular contributionsMonte Carlo rangeToday's dollars

Your plan

Starting amount

Monthly contribution

Expected annual return (%)

Years

Show results in today's dollars

Contributions are made monthly and compounded annually.

Balance in 30 years

$682,561

$10,000 start + $180,000 contributed + $492,561 growth — about 72% of the total is compound growth.

Growth over time

Shaded = your contributions · full height = balance incl. growth

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How this calculator works

Start with a lump sum, add a monthly contribution, and pick a return and time horizon. The average view compounds it year by year and shows how much of your final balance comes from contributions versus growth.

The Monte Carlo view replaces the single smooth return with 5,000 simulated market histories, so you see a realistic range instead of one optimistic line. It's the honest way to picture an uncertain future — and the seeded engine means the same inputs always reproduce the same range.

Compound growth

See returns compounding on a growing balance.

Contributions vs. growth

The chart splits what you put in from what the market added.

Realistic range

Monte Carlo shows the 10th–90th percentile outcomes.

Today's dollars

Optional inflation adjustment for real buying power.

Good to know

The Monte Carlo median usually sits below the average line. That's volatility drag, not a bug — a single average tends to look optimistic.

Results are very sensitive to the return assumption. Small changes compound into big differences over decades.

This doesn't model taxes, fees, or changing contributions over time.

It's a projection, not investment advice.

✓No account or sign-up required

✓Seeded, reproducible simulation

✓Shareable, exportable results

Frequently asked questions

How does compound growth work?+

Your returns earn returns. Growth is added to the balance each period, and the next period's growth is figured on the larger balance — so over long horizons, most of the final total can come from growth, not contributions.

What return should I assume?+

No single right number. A diversified portfolio has historically returned ~6–8% before inflation over long periods, but the future is uncertain. Try a range, and use the Monte Carlo view to see how volatility widens outcomes.

What does the Monte Carlo view show?+

5,000 simulated market histories with year-to-year variation, reported as a range: worst 10%, median, best 10%. The median usually sits below the simple average — that's normal volatility drag.

Should I adjust for inflation?+

Turn on 'today's dollars' if you want the result in real buying power; the portfolio then grows at your return minus inflation. Off shows the nominal future-dollar balance.

Put it to work

See how this growth fits your retirement and financial-independence plans.