Last updated: May 2026. Reviewed against IRS 2026 IRA contribution limits and Roth IRA phase-out ranges.
Growth projection formula
Annual mode starts with the current Roth IRA balance, applies the expected annual return, and then adds that year's
contribution at year end. The future value is equivalent to compounding the starting balance by
(1 + r)^n and adding a year-end contribution stream over the same number of years. This is why the
default case of $10,000 starting balance, $7,500 annual contributions, 30 years, and 7% return rounds to about
$784,578.
Annual vs monthly contribution timing
Monthly mode divides the annualized contribution by 12, applies a monthly return of the annual return divided by 12, and adds the monthly contribution after each monthly growth step. For example, $7,500 per year becomes $625 per month. Monthly mode usually produces a higher ending balance than annual year-end mode because deposits enter earlier throughout each year.
Inflation adjustment
The default display shows nominal future dollars. When "Show in today's dollars" is enabled, each displayed value
is divided by (1 + inflation rate)^years. With 3% inflation over 30 years, a nominal $784,578 result
is shown as roughly $323,000 in 2026 dollars. This does not forecast inflation; it simply converts the nominal
projection into a purchasing-power estimate using the user's input.
Retirement target estimate
The retirement target calculator starts with Roth IRA assets plus other retirement assets, compounds them monthly,
and adds monthly Roth and non-Roth savings after each monthly growth step. It converts each year-end balance into
2026 dollars using the inflation rate input. The target portfolio is annual spending / withdrawal rate.
For example, $60,000 of annual spending at a 4% withdrawal rate requires about $1.5 million in 2026-dollar assets.
This target mode is a deterministic planning estimate. It does not include Social Security, pensions, taxes on taxable or traditional-account withdrawals, healthcare costs, debt payments, market sequence risk, or Monte Carlo success probabilities.
Traditional IRA after-tax estimate
The main growth calculator includes a simple traditional IRA after-tax estimate by applying the selected future tax rate to a pre-tax balance. The dedicated Roth vs Traditional calculator goes further: it compares Roth savings with a traditional IRA path and can optionally invest the current-year tax savings in a taxable side account. That side account uses the selected capital gains rate when estimating its after-tax value.
Roth vs taxable brokerage model
The Roth path compounds without annual tax drag and treats qualified retirement withdrawals as tax-free. The taxable path separates dividend yield from price growth, taxes dividends each year before reinvestment, tracks basis, and applies long-term capital gains tax to remaining gains at the end. It does not model state taxes, fund turnover, tax-loss harvesting, wash-sale rules, charitable giving, or changing future tax law.
Eligibility phase-out formula
The eligibility checker compares MAGI with the IRS phase-out range for the selected tax year and filing status. Inside the range, it reduces the maximum contribution proportionally, rounds the reduced contribution up to the next $10 step, and applies the IRS $200 minimum when a reduced contribution is still allowed. Married filing separately has two paths: taxpayers who lived with a spouse use the $0-$10,000 range, while taxpayers who lived apart for the entire year use the single/head-of-household range.
2026 IRA contribution limits
The calculator uses the 2026 IRA limit of $7,500 for people under age 50 and $8,600 for age 50 or older, including the $1,100 catch-up amount. Source: IRS IR-2025-111.
Limitations
The calculators are educational estimates. They do not guarantee investment returns, verify taxable compensation, replace IRS worksheets, model all state taxes, handle every withdrawal exception, predict future contribution limits, or determine whether a backdoor Roth conversion is appropriate. Treat the output as a way to compare assumptions, not as tax, legal, investment, or financial advice.