Calculateur d'Intérêts Composés
Calculez la puissance exponentielle des intérêts composés sur votre épargne mensuelle. Modélisez votre indépendance financière.
Lisez aussi: Guide complet du calculateur, Intérêts composés expliqués, Guide DCA, Juros compostos explicados, Calculadora DCA, Calculadora FIRE
Comment ça marche
A compound interest calculator projects balance growth with monthly contributions and your chosen compounding frequency.
Les intérêts composés réinvestissent les gains. Ex. : 10 000 € à 7 %/an → environ 76 123 € en 30 ans ; avec 500 €/mois, environ 566 764 €.
Croissance avec apports mensuels
Les intérêts composés se calculent sur capital plus intérêts accumulés. Les apports mensuels et les années comptent plus qu'optimiser le taux la dernière année.
Capitalisation mensuelle vs annuelle change le solde final au même taux nominal—alignez la fréquence entre produits.
Inflation et impôts sur comptes imposables non déduits—réduisez le taux pour des scénarios réalistes.
Guide, exemples et méthodologie
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.
Related calculators
- Calculateur DCA
- Calculateur de Dividendes
- Calculateur d'Emprunt sur Plan Epargne Retraite (PER / 401k)
- Calculateur Retraite
Questions fréquentes
What is the compound interest formula?
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.
Comment fonctionnent les intérêts composés ?
Les intérêts portent sur le capital et les intérêts déjà acquis — d'où l'accélération de la courbe.
Que deviennent 500 €/mois sur 30 ans ?
À environ 7 %/an : 500 €/mois sur 30 ans ≈ 566 764 € — testez votre scénario.
Commencer à 25 ou 35 ans : quelle différence ?
Dix ans de capitalisation en plus comptent souvent plus qu'un petit gain de rendement.