DinoStacks The real math on getting rich.

Compound Interest Calculator

The engine behind every path.

The foundational calculation behind every path on this site: how deposits, return, and time turn into wealth. Includes monthly contributions and an inflation toggle.

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Final balance
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Total contributed
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Interest earned
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Enter your numbers to see the math.
This calculator produces estimates based on the assumptions you enter. Investment returns are not guaranteed and past performance does not predict future results. Actual results will differ.

What this calculator does

It projects the future value of a starting amount plus regular contributions, compounded at your chosen frequency, and shows the split between what you contributed and what the market returned — plus the inflation-adjusted value of the result.

The formula

FV = P(1+r/n)^(nt) + PMT · [((1+r/n)^(nt) − 1) / (r/n)]

where P is the initial deposit, PMT the periodic contribution, r the annual return, n the number of compounding periods per year, and t the number of years.

Worked example

$5,000 initial, $500/month, at 7% for 20 years compounds to roughly $280,000 — of which about $125,000 is your own contributions and about $155,000 is growth. The growth exceeds your contributions because of compounding; the gap widens dramatically the longer you wait.

Assumptions & limitations

  • Default return is 7% real (after inflation) (Investopedia 6.81%; SmartAsset 6.5%; multiple sources ~6.5–7% (1928–2024)).
  • Returns are assumed constant and reinvested; real returns vary year to year.
  • Taxes and fees are not modeled — use tax-advantaged accounts and low-cost funds to keep them small.
  • This is an estimate, not a guarantee. BLS CPI long-run average for the inflation adjustment.

FAQ

What does "compound interest" actually mean?
It means earning returns on your returns. In year one you earn a return on your principal; in year two you earn a return on the principal plus last year’s gains. Over decades this snowball is the single most powerful force in wealth-building — but it is slow at first, which is why it is underrated.
Why does monthly vs daily compounding matter so little?
At normal return rates, the difference between monthly and daily compounding is tiny — fractions of a percent over decades. The far bigger levers are the contribution size, the return rate, and especially the time horizon.
Is my money safe in this calculation?
No — this is an estimate of a volatile asset, not a bank account. The stock market loses money in roughly 1 in 4 calendar years and can drop 35% or more in a bear market. The long-run average is real, but the path is bumpy.

See the full context: How to make a million through index investing →

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