Roth IRA calculator
Two questions. What a Roth IRA grows to by the time you retire, and what it cost if you opened one, kept contributing, and never actually bought anything. The second one uses what the S&P 500 and the total market actually did, month by month, not a smooth rate.
Every number below is arithmetic on the inputs you type. The defaults are example inputs, not a forecast. Change them.
Your plan
Balance by year
The brown line is the same money in a plain brokerage account, with the tax rate you set taken off the gains at the end. Real taxable accounts also pay tax on dividends along the way, so the true gap is a little larger than drawn.
Year by year
| Year | Age | Put in so far | Growth that year | Balance |
|---|
The account that never bought anything
Month by month, as it actually happened
Year by year
| Through | Put in so far | Cash | Invested | Gap |
|---|
How the numbers are built
The projection adds one twelfth of the yearly contribution at the start of every month and compounds the balance monthly at the return you set. The taxable comparison runs the same money the same way and takes your tax rate off the gains at the end, which is the simplest fair version and slightly flatters the taxable account. The Roth advantage is the difference.
The cash mode uses month-end prices for VOO and VTI with every distribution reinvested, so each month’s return is the fund’s total return for that month. The contribution lands at the start of the month and earns that month. Cash earns the effective federal funds rate for the same month, divided by twelve, or nothing, or a rate you set. Both paths get identical contributions on identical dates; the only difference is whether the money was ever invested.
Contribution limits. The IRS limit for 2026 is $7,500, or $8,600 if you are 50 or older, and it is lower if your taxable compensation is lower. The projection flags a figure above the limit for your age and otherwise leaves your number alone, because the limit changes most years and you may be modelling more than one account.
Every figure is nominal. No inflation adjustment, no fees, no fund expense ratio, no tax on the cash interest, which in a Roth there would not be.
Sources
Contribution limits: IRS, Retirement topics, IRA contribution limits, page updated 2026-08-03, read 2026-09-07. Fund returns: month-end adjusted closes for VOO (from October 2010) and VTI (from June 2001) via the Alpha Vantage TIME_SERIES_MONTHLY_ADJUSTED endpoint, read 2026-09-07; the series here run January 2011 and January 2002 through August 2026, the last complete month. Cash: effective federal funds rate, monthly, FRED series FEDFUNDS via Alpha Vantage, read 2026-09-07. The raw pulls and the script that turns them into the series on this page are in the site’s repository under research/roth-cash-drag/.
Where to go next
- All the free tools Options, futures, dividend, stock average, margin call and net worth calculators, none of them gated.
- Dividend calculator Reinvesting against taking the cash, year by year, with an income target.
- Net worth calculator Everything you own minus everything you owe, including the retirement accounts.
- The beginning The first entry in the trading journal, before any of the tools existed.
- Money management The rest of this section.
Eligibility to contribute to a Roth IRA depends on your filing status and income, and this page does not check that. Nothing here is investment, tax or legal advice, a recommendation, or a solicitation.