Tool · Decision Aid
Roth vs. Traditional, when rates move
With Roth, you pay income tax before contributing. A deductible Traditional contribution saves tax now, but withdrawals are taxable later. Compare those two paths using tax rates you choose. You can also explore investing the deduction’s savings and an optional required-withdrawal illustration. This is not a full retirement tax plan.
New to the difference? Start with the plain-English Roth IRA vs. Traditional IRA comparison, then come back to run your own numbers.
Corrected September 4, 2026: Required-withdrawal calculations and model scope corrected. View correction history.
All calculations run locally in your browser. Your inputs are never transmitted or stored.
Before you start
These examples assume the entire Traditional contribution is deductible and that Roth withdrawals qualify to be tax-free. Contribution limits and eligibility are not enforced. A result is a what-if comparison, not permission to contribute or a recommendation to switch accounts.
Check contribution eligibility and Traditional deduction rules first.
1 · The contribution
The net cost after any deduction: Roth gets this amount; Traditional gets budget ÷ (1 − current rate). Check that both resulting contributions fit your legal limit.
A hypothetical annual amount, held constant. The IRA limit for 2026 is $7,500, or $8,600 at age 50+. Actual compensation, eligibility and combined contribution limits still apply.
Deposits at the start of each year; comparison at that period’s end.
Mode C only. No living expenses are withdrawn; net RMDs are reinvested.
The illustration begins in 2027 with no existing balance. This sets your RMD age cohort; it is not an inherited-IRA calculator. Mode C uses the Uniform Lifetime Table, not the special table for a sole-beneficiary spouse more than 10 years younger.
2 · Tax rates
Combined federal + state on the last dollar.
Assumed rate on these withdrawal dollars—not your average rate on all income. Brackets are not calculated.
LTCG rate applied to the side account's gains at liquidation.
Hypothetical annual reduction in return. The side-account model is approximate; it does not track individual tax lots.
3 · Growth
Nominal, pre-tax. Same rate applied to Roth, Traditional, and the side account.
What is outside this model?
Social Security taxation, Medicare income-related surcharges (IRMAA), state-specific exemptions, tax credits and inheritance taxes are not calculated. If you expect to move, reflect the assumed state difference in the two combined tax rates above.
Illustrative after-tax value
Traditional is actually two pools
Traditional IRA (after retirement tax)
Remaining pre-tax IRA balance × (1 − assumed withdrawal tax rate).
Side account (after LTCG tax)
Tax savings from deduction, invested in taxable brokerage, liquidated at end.
Traditional total
Year-by-year projection
Yellow rows: RMDs begin · Green: Roth overtakes| Year | Age | Roth (qualified value) | Trad IRA (pre-tax) | Required withdrawal | Side account (after gain tax) | Trad total after tax | Difference (Roth − Trad) |
|---|---|---|---|---|---|---|---|
What could flip the call
Beyond the headline rate comparisonHow sensitive is this answer?
One-input-at-a-timeBreak-even retirement rate
Rate in retirement where Roth and Traditional tie.
Break-even current rate
Your current rate where the tool would flip.
Horizon effect (RMD only)
Projection years with required distributions; Mode C only.
User Guide
How to use the Roth vs. Traditional Comparator
Think of this as a tax-rate experiment. It can show how assumptions change an answer; it cannot tell you what your future tax rate will be.
Choose the question you want to answer
- Equal after-tax burden: “What if either choice costs me the same amount after the deduction?” At equal tax rates, identical growth produces a tie. A longer horizon alone does not overturn that identity.
- Full contribution + side account: “What if I put the same amount into either IRA and invest every dollar of the Traditional deduction’s tax savings?” The extra taxable account is included in Traditional’s total.
- Extended horizon with RMDs: “What if I leave the money invested after contributions stop and reinvest required withdrawals?” A required minimum distribution, or RMD, is a minimum amount a Traditional IRA owner must take out at the applicable age. This mode is not a retirement spending plan.
Start with a simple example
Suppose both tax rates are 25%, growth is 0%, and you contribute for one year. With a $750 after-tax budget, Roth gets $750. A fully deductible $1,000 Traditional contribution costs the same net $750; after $250 of withdrawal tax, it also leaves $750. Change the future rate to 20%, and Traditional leaves $800. These are hypothetical amounts, not annual limits.
Use the result as a starting point
First confirm whether a Traditional deduction and direct Roth contribution are available to you. Then try several reasonable future tax rates. The break-even cards show the assumed rate where the modeled totals tie; they do not forecast your tax bracket.
Returns are nominal (not adjusted for inflation). Contributions, tax rates and returns are held constant. Beginning-of-year deposits get a full year of growth. Modes A and B stop when contributions end; only Mode C uses the extra-year input.
The tool omits Social Security tax changes, Medicare IRMAA, living expenses, actual tax brackets, state-specific rules and inherited-account treatment. Those can matter, so the larger number is not a personal recommendation. A mix of account types may serve goals that this simple calculation cannot measure.
Methodology & sources
The formulas, spelled out
Contribution and side-account formulas
For annual beginning-of-year deposits, define F(A,r,n) = A × [(1+r)n − 1] ÷ r × (1+r). When r is zero, F = A × n.
Mode A: Roth = F(budget,r,n). Traditional = F(budget ÷ (1−current rate),r,n) × (1−withdrawal rate). Both are valued when contributions stop. The full Traditional deduction and tax-free qualified Roth withdrawal are assumed.
Mode B: Roth = F(contribution,r,n). Traditional = F(contribution,r,n) × (1−withdrawal rate) plus a side account. Annual side deposits = contribution × current rate. They earn r minus the entered annual drag; negative net returns are allowed. The terminal capital-gains tax applies only to a positive amount above modeled side-account basis.
The side account is a simplified return-haircut model, not tax-lot accounting. Its basis is the sum of deposits; tax basis changes from reinvested taxable distributions are not tracked. The result should not be read as a tax-return estimate.
Mode C: timeline and required withdrawals
The projection starts in 2027 with zero balances. At each year’s start it deposits the contribution and deduction savings, if that year is within your contribution period. Growth occurs during the year. Any RMD is based on the prior December 31 Traditional balance divided by that year’s Uniform Lifetime factor, and is taken at year-end. Its after-tax amount is added to the side account and its basis.
RMDs begin at age 73 for people born in 1951–1959 and age 75 for those born in 1960 or later. The entered age at the end of 2026 identifies the cohort. The model uses the standard Uniform Lifetime Table, including its age-120-and-over factor. It does not use the special joint-life table, inherited-account rules or first-RMD postponement.
Roth IRAs have no lifetime RMDs for their original owner. This illustration leaves both paths otherwise untouched: no spending, voluntary withdrawals or conversions. Remaining Traditional dollars are valued after the entered withdrawal rate; the side account is valued after assumed gain tax. Yearly rows and the final totals use the same calculation.
Break-even, eligibility and limits
Break-even rates are solved between 0% and 50%, holding all other inputs fixed. “n/a” means no unique crossing in that range. These are assumption changes, not predictions.
The tool does not calculate contribution eligibility, deductibility, progressive tax brackets, Social Security tax, IRMAA, tax credits, state-specific rules, employer matching, after-tax Traditional basis or inheritance tax. It does not grow future contribution limits. Check the legal limits independently, especially when Mode A grosses up a budget.
Primary sources
- IRS Publication 590-A: IRA contribution and deduction conditions.
- IRS Publication 590-B: qualified Roth distributions, prior-year-end RMD balance and Uniform Lifetime Table.
- IRS Publication 550: taxable investment income and capital gains.
- IRS Publication 915: Social Security tax depends on other income; a flat 85%-of-benefits surcharge is not a substitute for that calculation.
- SECURE 2.0 §107 and IRC §401(a)(9): birth-cohort RMD ages.
Reviewed September 4, 2026. The sources establish the tax rules, not future tax rates or investment returns.
Corrections and updates
September 4, 2026: Corrected required withdrawals to use the prior year-end balance and completed the lifetime divisor table. Removed a fixed Social Security tax surcharge that did not calculate actual benefit taxability, along with unsupported controls. The comparison and break-even result now use the same scenario. Clarified the timeline, deduction assumptions and omitted tax effects, and replaced an inaccurate worked example.