A US-localised calculator pre-filled in USD. Use it to project growth inside a 401(k), Roth IRA, HSA, or taxable brokerage over typical American working-life horizons.
A $10,000 Roth IRA balance plus $500/month at 7% for 30 years compounds to roughly $640,000 — all of which is tax-free at withdrawal after age 59½, because Roth contributions were made post-tax.
The 2026 401(k) contribution limit is $24,500 ($32,000 if age 50+); the Roth IRA limit is $7,500 ($8,500 if 50+) and phases out at higher incomes. This calculator does not enforce limits — it is a growth projection.
Compound interest is interest earned on interest. Each period, your balance grows by the previous balance times the periodic rate, then your contribution is added. Over decades the compounded portion dwarfs the contributed portion — the "hockey stick" curve every personal-finance article keeps showing you.
P is your starting amount. PMT is each monthly contribution. r is the monthly rate (annual ÷ 12). n is the total number of months.
In a US context: Roth IRA and Roth 401(k) growth is tax-free at qualified withdrawal, so the nominal number this calculator shows is close to your real take-home. Traditional 401(k) and IRA withdrawals are taxed as ordinary income in retirement. HSA growth is triple tax-advantaged for qualified medical expenses. In a taxable brokerage, long-term capital gains rates (15–20%) reduce effective returns — model with a rate ~1–2% lower.
Important: figures are nominal — they don't subtract US inflation. To see real growth, subtract a 2–3% CPI estimate from your return assumption.
Compound interest is interest earned on both your original deposit AND on the interest already credited. It causes balances to grow faster over time — the longer you leave money invested, the more dramatic the effect.
Future Value = Principal × (1 + r)n + PMT × ((1 + r)n − 1) / r, where r is the periodic interest rate (annual rate ÷ 12 for monthly compounding) and n is the total number of periods.
For a target-date or broadly diversified index fund inside a 401(k), 6–8% annualised is a common historical assumption. Money market and bond funds run lower. This calculator does not promise any specific return — model multiple scenarios.
No — the figures shown are nominal. To see real (after-inflation) growth, subtract a US CPI estimate (typically 2–3%) from your assumed return rate before entering it.
Inside a Roth IRA or Roth 401(k), all growth and qualified withdrawals are tax-free. Inside a traditional 401(k) or IRA, contributions are pre-tax but withdrawals are taxed as ordinary income. Inside an HSA, growth is triple tax-advantaged for qualified medical expenses. In a taxable brokerage, long-term capital gains (15–20%) and qualified dividend rates apply — model with a return rate roughly 1–2% lower.
ProFinanceCast turns one-off calculations into a living 10-year forecast that updates as your income, expenses, and goals change. Free forever for the core forecast.