Roth or traditional comes down to one question, whether your tax rate will be higher now or in retirement. Every rule of thumb about the choice is a guess at that number. RetirFi's IRA Calculators tab prices the bet with your own numbers instead. It holds two tools. The Contribution calculator compares the two account types using your rates, growth, and timeline, and the Conversion planner reads your Monte Carlo simulation year by year to find the cheapest years to move money that already sits in a traditional account. This article explains what each tool computes and how to read the results.
The rule underneath both tools
A traditional contribution is deducted from your taxable income today and taxed as ordinary income when withdrawn. A Roth contribution is taxed today and comes out tax-free once the account has been open five years and you are at least 59½. Traditional accounts also carry required minimum distributions, forced taxable withdrawals that begin at age 73 (75 for those born in 1960 or later, under the SECURE 2.0 Act). A Roth IRA has none.
The core trade-off. Traditional saves you tax at today's rate. Roth saves you tax at your future rate. Whichever rate is lower is the account that wins.
The Contribution calculator
The tool answers one question. For the same dollars into each account every year, which leaves more after-tax spending money at retirement? Five inputs drive it, and every one auto-fills from your plan. They are your annual contribution, years until retirement, growth rate, tax rate today, and tax rate in retirement. A badge next to each field names its source ("your marginal rate", "retire at 65"), and typing over any value turns it into a what-if you can undo with one click.
The retirement tax rate is the input worth watching, because it is the number the whole bet turns on. After you run a simulation, the field uses the effective federal rate along your median Monte Carlo path, total retirement tax divided by the gross income that funded your spending. Our Monte Carlo explainer covers how those simulated paths are generated. Without a run, the field falls back to a bracket estimate from your spending goal and Social Security.
The comparison is built to be apples-to-apples. Contributing the same amount to each account is not the same sacrifice, because the traditional contribution is deductible and the Roth one is not. The tool therefore credits the traditional side with its upfront tax savings, the contribution times your current rate, and invests that money in a taxable side account growing at the same rate, with a 15% capital-gains tax on its gains at the end. Uncheck "invest the savings" and the deduction is treated as spent, which is what many savers do with it in practice.
The numbers below come straight from the tool. Put $7,000 a year into each account for 25 years at 7% growth and both balances reach $442,743 before tax. The two rates decide what you keep. Each row assumes the full tax savings gets invested.
| Rate now | Rate in retirement | Traditional after tax | Roth after tax | Margin |
|---|---|---|---|---|
| 22% | 12% | $478,182 | $442,743 | Traditional by $35,439 |
| 22% | 22% | $433,908 | $442,743 | Roth by $8,836 |
| 12% | 22% | $393,650 | $442,743 | Roth by $49,094 |
The middle row is the instructive one. Equal rates do not produce a tie, because contribution limits are set in dollars while a Roth dollar is worth more after tax, the same reason our guide to estimating your retirement number counts a Roth dollar as more valuable when sizing a portfolio. The traditional side's entire edge lives in its taxable side account, and that account pays capital-gains tax; the $8,836 margin is exactly that tax. Spend the deduction instead of investing it and traditional loses all three rows.
The Conversion planner
A Roth conversion moves money out of a traditional account into Roth, paying ordinary income tax now to avoid it later. What a conversion costs depends almost entirely on which year you do it in, and future years are a forecasting problem. The planner reads the median path of your latest Monte Carlo run to solve it, pulling your earned income, required distributions, the taxable share of your Social Security, and your pre-tax balance for every year of the plan. It stays locked until you run a simulation.
From that timeline it flags your low-income window, the years after you retire but before required distributions begin, when a conversion stacks on the least other income. It then fills each window year up to the top of a bracket you pick. The default target matches your simulated retirement rate, because converting at a rate above the one you would pay anyway usually costs more than it saves. Each row of the schedule stacks its conversion on that year's other income and prices it with the actual bracket math, so you see the tax, the effective rate, and the bracket the conversion tops out in. The schedule stays editable. Click years in or out, type your own amount into any row, and the totals recompute.
The payoff table then compares two futures for the converted dollars at your plan's horizon. Converted, they compound tax-free with no required distributions. Left in traditional, RMDs force them out from age 73 or 75, taxed at each year's marginal rate stacked on your simulated income, with the after-tax remainder reinvested in a taxable account. Our guide to required minimum distributions covers why those forced withdrawals sting. Leaving "pay the conversion tax from outside cash" checked keeps the comparison on equal dollars; the convert column keeps the full amount compounding, and the leave column gets credit for investing the tax cash it kept.
What the tools assume
Both calculators use 2024 federal brackets and a single 15% capital-gains rate, and neither writes anything back to your plan. They ignore state tax, IRMAA surcharges, ACA subsidies, the five-year rule on conversions, and IRA deduction phase-outs. The results are educational estimates, not tax advice; check a multi-year conversion plan with a professional before you execute it.
The bottom line
The direction of your tax rate decides the contribution question, and the calculator prices it in dollars instead of leaving it as a rule of thumb. The conversion question is about timing, and the planner finds the window by simulating your retirement instead of assuming it. Both tools run on the plan you have already entered. Open the calculator, add your accounts, run a simulation, and the IRA Calculators tab fills itself in. The user guide documents every field if you want the fine print.
Sources
Put the theory into practice.
Enter your Roth and traditional balances, your spending, and your timeline, then run a Monte Carlo simulation to see how the tax-aware drawdown plays out for you.
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