A compound interest calculator projects balance growth with monthly contributions and your chosen compounding frequency.
Zinseszins verzinst Kapital plus bereits erzielte Zinsen. Beispiel: 10.000 € zu 7 % p.a. → ca. 76.123 € in 30 Jahren; mit 500 €/Monat ca. 566.764 €.
Wachstum mit monatlichen Einzahlungen
Zinseszins berechnet auf Kapital plus bereits aufgelaufene Zinsen. Monatliche Einzahlungen und Jahre am Markt zählen mehr als Rate-Optimierung im letzten Jahr.
Monatliche versus jährliche Verzinsung ändert das Endkapital bei gleichem Nominalzins—Frequenz beim Produktvergleich angleichen.
Inflation und Steuern auf taxable Konten nicht abgezogen—Rate für realistische Szenarien reduzieren.
Leitfaden, Beispiele und Methodik
How to use this compound interest calculator
Enter your starting balance, optional monthly contribution, expected annual return, compounding frequency, and years invested. Results update instantly in your browser. Use monthly compounding when modeling most US brokerage or high-yield savings assumptions; use annual only if that is how your product quotes the rate.
Example (USD)
Input
Value
Result after 30 years (7% annual, monthly compound)
Starting balance
$10,000
$76,123 (no extra deposits)
Plus $500/month
Same rate
~$566,764 total
Interest earned
—
~$386,764 on top of $180,000 contributed
How we calculate
Lump-sum growth uses A = P(1 + r/n)^(nt). Each monthly contribution is compounded from its deposit date to the end of the horizon, then summed. We do not deduct taxes, fund expense ratios, or inflation unless you lower the return yourself. For purchasing-power planning, subtract an inflation assumption from your nominal return (e.g. 7% nominal minus 3% inflation ≈ 4% real).
Common mistakes
Quoting a yearly APY while the account compounds daily or monthly (understates growth).
Ignoring ongoing 401(k) or IRA fees when comparing to a headline market return.
Assuming you can keep max contributions every year without a cash-flow plan.
Comparing to a CD or Treasury without matching the same time horizon.
Monthly contributions vs lump sum (US portfolios)
Most US retirement savers compound through payroll 401(k) deferrals plus employer match. A $500/month contribution at 7% nominal over 30 years can exceed $560,000—often more impactful than optimizing a single year's return. Use this calculator to test sensitivity: raise contributions 1–2% before chasing an extra 0.5% fund return.
Real vs nominal returns
Headline market returns are nominal. If inflation averages 3% and your portfolio earns 7%, your real return is about 4%. For goals stated in today's dollars (e.g. $1M nest egg), subtract an inflation assumption from the return field or run a second scenario at a lower rate.
Who should use this calculator
Use it for HYSA projections, taxable brokerage goals, 529 planning, or back-of-envelope retirement checks. Pair with our retirement and FIRE calculators when the question is sustainable withdrawal, not just accumulation. Pair with DCA calculator when deciding whether to invest a windfall all at once or over months.
For a single deposit: A = P(1 + r/n)^(nt), where P is principal, r is the annual rate as a decimal, n is compounding periods per year, and t is years. With monthly contributions, each deposit has its own timeline; this calculator totals them.
How much does $500 a month grow in 30 years?
At about 7% average annual return with monthly compounding, $500/month for 30 years is roughly $566,764 total (about $180,000 contributed). Your starting balance and actual return change the outcome.
Wie funktioniert Zinseszins?
Zinsen werden auf Kapital plus bereits gutgeschriebene Zinsen berechnet — deshalb beschleunigt sich das Wachstum.
Was werden 500 €/Monat über 30 Jahre?
Bei ca. 7 % p.a.: 500 €/Monat × 30 Jahre ≈ 566.764 € — passen Sie Rendite und Startkapital an.
Mit 25 vs. 35 anfangen — wie groß ist der Unterschied?
Zehn Jahre mehr Laufzeit schlagen oft eine etwas höhere Rendite.