How to read the 401(k) & IRA calculator

Project one tax-advantaged account to retirement, compare future Roth and traditional contributions on equal out-of-pocket cost, or estimate required minimum distributions from modeled tax-deferred money.

What it calculates

The calculator carries one 401(k), Roth 401(k), traditional IRA, or Roth IRA from the current age to the retirement age. Each month it adds the employee contribution and any modeled employer contribution, applies growth, and keeps already-taxed Roth money separate from tax-deferred money.

That separation lets the page show both a gross balance and an estimated after-tax value. It also supports an equal-cost Roth comparison and an RMD projection while preserving the different tax treatment of each balance.

Questions it answers

What it grows to

Projects the selected account to the retirement age. The headline after-tax value subtracts the retirement tax rate from modeled tax-deferred money while leaving Roth money untaxed for a qualified withdrawal.

Roth vs. traditional

Compares where future contributions go while leaving money already saved in its existing tax bucket. The traditional side invests its current tax saving in a taxable side investment to keep the strategies’ out-of-pocket costs equal.

Required distributions

Projects the modeled tax-deferred balance and applies the IRS Uniform Lifetime Table from the applicable start age. Traditional IRAs cannot use the modeled still-working delay; workplace plans expose that policy explicitly.

Major inputs

Account and opening balance: The account selects Roth or deferred treatment, whether an employer can contribute, and which model limit applies. A Roth 401(k) also accepts a separate pre-tax employer balance. In RMD mode, enter the pre-tax balance on the prior December 31, as dated on the form (December 31, 2025 for tax year 2026). Verify retained amounts when changing modes or tax years; Roth funds remain excluded from RMDs.
Starting tax year, current age, birth year, and retirement age: The tax year and birth year determine the age reached during each contribution year, including catch-up eligibility. The form requires those fields to be coherent. Birth year also determines the statutory RMD age; the end age controls how long distributions are shown.
Salary and annual pay rise: Employee and employer percentages are applied to salary. A pay-rise assumption changes future dollar contributions, subject to the modeled account limit.
Your contribution: The percentage of salary you elect to contribute. The calculator caps employee dollars at its account limit and calls out years in which the desired amount is capped.
Employer match: The employer percentage applied to the eligible portion of your contribution. “50% of the first 6%” means a 50% match rate and a match limit of 6% of salary.
Tax rate now: The marginal rate the model uses for the tax saving on a traditional contribution and for tax drag on growth in the comparison's taxable side account.
Tax rate in retirement: The flat rate applied to the entire modeled deferred balance or RMD. Real withdrawals can cross brackets and face different federal and state treatment.
Return and inflation: The return grows balances at one steady rate. Inflation restates retirement values in today's money and raises the calculator's modeled contribution limits over time.

What the results mean

Gross balance: The account value before tax due on a later withdrawal. It can overstate spendable value when much of the balance is tax-deferred.
After-tax value: Roth balance plus taxable side investment plus the deferred balance after the entered retirement tax rate. It is a common-dollar comparison, not a tax return calculation.
Your contributions: The cumulative employee dollars deposited after annual limits. It does not include the starting balance or employer contributions.
Employer contributions: The cumulative amount the employer adds under the match assumptions. It is compensation from the plan, not part of your out-of-pocket cost.
Taxable side investment: On the traditional side only, the current tax saving is invested outside the retirement account. Its gains are reduced by the current tax-rate assumption as they accrue.
Break-even retirement tax rate: The modeled future withdrawal-tax rate at which Roth and traditional after-tax values are equal. Above it Roth leads in this comparison; below it traditional leads, subject to the model's other assumptions.
Required distribution: The applicable prior year-end deferred balance divided by the IRS life-expectancy factor. The calculator also estimates flat-rate tax, after-tax proceeds, and the remaining balance.
In today's money: The future nominal value discounted by the inflation assumption. Use it to compare a retirement-age balance with purchasing power today.

Worked example

Thirty years of 401(k) saving

Hypothetical example: a 35-year-old born in 1991 has $50,000 in a traditional 401(k), earns $100,000, contributes 10%, and receives a 50% match on the first 6% of salary. Salary growth and inflation are 0%; the account earns 7%; current and retirement tax rates are 24% and 22%; retirement is at 65 and the RMD projection ends at 95.

Question	Modeled answer	Interpretation
What it grows to	$1,654,683 gross; $1,290,653 after tax	The model includes $300,000 of employee contributions, $90,000 of employer contributions, the $50,000 start, and about $1,214,683 of growth.
Roth vs. traditional	Roth $1,506,265; traditional $1,462,744, after tax	Roth leads by about $43,520 at a 22% retirement tax rate. The modeled break-even retirement tax rate is about 17.6%.
Required distributions	First modeled RMD at 75: about $132,318	The modeled opening deferred balance is about $3,255,012. At a 22% tax rate, estimated tax is about $29,110 and net proceeds about $103,208. This assumes no earlier withdrawal from the modeled deferred balance.

The Roth comparison changes the treatment of future employee contributions. The existing $50,000 remains deferred in both columns because converting it would be a separate taxable event. The calculator also keeps the modeled employer match deferred, so even its Roth 401(k) column contains some deferred money.

Assumptions and limitations

Contribution limits are a dated model input

The calculator uses the published 2025 and 2026 schedules. For 2026 it models the $24,500 workplace and $7,500 IRA base limits, the $8,000 and $1,100 ordinary catch-ups, and the $11,250 workplace catch-up at ages 60 through 63. It also applies the eligible-compensation and annual-additions ceilings. For the 2026 mandatory Roth catch-up source, projected salary is used as a planning proxy for the prior-year FICA wages the actual rule tests. Later unpublished years are estimates indexed and rounded from the latest known schedule, not enacted limits. Check the current IRS limits table before making a contribution decision.

Employer matches can have different tax treatment

The calculator models every employer match as tax-deferred, including a match associated with Roth 401(k) contributions. Under IRS SECURE 2.0 guidance, a qualifying plan may permit a fully vested matching or nonelective contribution to be designated Roth. Your plan document and election control; the calculator does not model that alternative.

Required minimum distributions have account-specific rules

The calculator uses age 73 for birth years 1951 through 1959 and age 75 from 1960 onward, with the IRS proposed treatment of the statutory overlap for 1959. It uses the Uniform Lifetime Table. A spouse more than ten years younger who is the sole beneficiary can require another table, and inherited accounts follow different rules.

Traditional IRA distributions start at the modeled birth-cohort RMD age even if retirement is later. A workplace plan can instead use the explicit still-working delay through the entered retirement age. That policy is subject to plan terms and exceptions such as 5% ownership; confirm the account type and date with the custodian, plan administrator, or a qualified tax professional.

Current IRS RMD guidance says owner RMDs are not required from Roth IRAs or designated Roth workplace accounts. The calculator excludes modeled Roth dollars but applies its RMD arithmetic to any balance it treats as tax-deferred, including its modeled tax-deferred employer match.

The model uses one steady return, one salary-growth rate, and flat current and retirement tax rates. It does not model brackets, state tax, capital-gains rates, withdrawal ordering, or market sequences.
It does not test Roth IRA income eligibility, traditional IRA deduction eligibility, early-withdrawal penalties, loans, after-tax contributions, conversions, or inherited-account rules.
An RMD is a minimum distribution, not necessarily spending. Money can be reinvested in a taxable account after distribution, but the calculator does not project that reinvestment.

Sources and further reading

Sources reviewed August 2026. These sources explain current federal rules and concepts; they do not endorse this calculator or its assumptions.

IRS: COLA increases for retirement-plan and IRA limits — current and historical annual contribution and catch-up limits.
IRS: Retirement plan and IRA required minimum distributions FAQs — covered accounts, timing, tables, tax treatment, designated Roth exemptions, and owner responsibility.
IRS Notice 2024-2 in Internal Revenue Bulletin 2024-02 — SECURE 2.0 guidance, including designated Roth matching and nonelective contributions.

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