How to Calculate Your Roth vs. Traditional Comparison Calculator Step‑by‑Step
- →Annual contribution (Traditional amount C) — The Traditional contribution used as C in both comparison framings.
- →Current age
- →Retirement age — Must be the same as or later than current age. Equal ages are a valid zero-year horizon.
- →Assumed annual return — A constant illustrative rate, not a forecast or guaranteed return.
- →Current marginal tax rate — Used to normalize take-home cost; full Traditional deductibility is assumed.
- →Retirement marginal tax rate — Applied to the projected Traditional balance in this simplified comparison.
Hidden Factors Most People Forget
Two Fair Ways to Compare Roth and Traditional
Choosing between a Roth and Traditional retirement contribution is a comparison of tax timing, not a contest between tax-free and taxable words. Traditional contributions may be deductible now, depending on the plan and circumstances, and distributions are generally taxed later. Roth contributions are made after tax; qualified withdrawals are generally tax-free. To make that tradeoff understandable, this estimator displays two framings: the same gross contribution and the same take-home cost. They are both useful, but they answer different questions.
Enter a Traditional annual contribution amount, your current age, a retirement age, an assumed annual return, and current and retirement marginal tax rates. The default example uses $6,000 per year, age 35 to 65, a 7% return, and 24% for both tax rates. The output is an illustration of repeated annual contributions, not an investment forecast, tax return or personalized recommendation. The same-cost result is highlighted because it makes the household cash-flow comparison explicit.
Framing One: The Same Gross Contribution
In the same-contribution framing, each account receives the same entered amount, called C, each year. The Traditional account accumulates C and its modeled balance is reduced by the entered retirement tax rate. The Roth account accumulates C and assumes qualified withdrawals are tax-free. Both use the same annual return and number of years. This view answers: if the same number of dollars is deposited into each account, what are the modeled after-tax balances?
For a concrete illustration, suppose C is $6,000, the time horizon is 30 years, the annual return is 7%, and the retirement tax rate is 24%. The accumulation factor is built one year at a time, with each deposit added at year-end. The gross value before tax is approximately $566,764. Applying a 24% retirement tax to the Traditional balance gives about $430,741 after tax; the Roth balance is about $566,764 if its withdrawal is qualified. That larger Roth value does not make this an equal-cost comparison: the Roth contribution uses more take-home pay today.
Framing Two: The Same Take-Home Cost
For a fair cash-flow comparison, the Traditional contribution remains C, while its assumed current tax deduction lowers the modeled annual take-home cost to C × (1 − current tax rate). The Roth deposit is normalized to that same cost: C × (1 − current tax rate). At a $6,000 contribution and a 24% current rate, the Traditional take-home cost is $4,560 per year, and the normalized Roth contribution is also $4,560 per year. The Roth account does not also receive another contribution of $6,000 or a separate investment of the tax difference.
With equal 24% current and retirement rates, same-cost outcomes match in this model. If the retirement rate is higher than the current rate, the normalized Roth outcome tends to be higher; if the retirement rate is lower, Traditional tends to be higher. The mechanism is visible in the math: both accounts receive deposits that cost the same today, then Traditional is taxed at the entered rate in retirement while qualified Roth withdrawals are not taxed. This clean result is useful for understanding the rate tradeoff, but real deductions and tax brackets are not always this simple.
How Growth and Time Are Calculated
The projection makes one end-of-year deposit in each modeled year. It starts with no balance, grows the prior balance by the entered constant return, then adds that year's contribution. In compact form: next balance = prior balance × (1 + return) + contribution. A 30-year horizon therefore contains 30 deposits, and the final deposit receives no growth during the year it is made. The tool builds an accumulation factor by repeating that operation, which also supports a zero return or a negative entered return without relying on a special annuity shortcut.
If current age equals retirement age, the horizon is zero. No deposits or investment growth are projected, so both account values are zero under this no-starting-balance model. The equality is valid and intentional, rather than an input error. Retirement age earlier than current age is invalid and the interface should show a clear warning instead of attempting a calculation. Ages are whole numbers from 18 through 100; return ranges from -20% to 20%, tax rates from 0% through 60%, and annual contribution from $0 through $1,000,000.
What the Model Assumes and Leaves Out
This comparison assumes full deductibility of the Traditional contribution at the entered current marginal rate, and assumes Roth withdrawals are qualified and tax-free. It uses the same constant return in either account. It excludes annual contribution limits, fees, employer matches, starting balances, inflation, plan-specific restrictions, contribution timing variations, other account assets and a brokerage investment of tax savings. Real Traditional withdrawals may not all face one marginal rate, and actual Roth withdrawals can be taxable or penalized if qualification rules are not met. Tax rates, law and investment returns can change substantially over a long horizon.
Neither framing models progressive brackets or calculates an actual tax bill. The same-cost formula treats the current rate as a direct reduction in take-home cost; it does not establish that a person receives the full assumed deduction. If you cannot deduct a Traditional contribution, the comparison changes. The model also ignores Social Security taxation, required distributions, state tax, early withdrawal rules, account conversions and the timing of withdrawals. Treat the values as a controlled illustration for comparing assumptions, not a promise of account value or a complete retirement plan.
Reading the Rows and Applying the Estimate
The comparison table first shows after-tax balances when both accounts receive C. It then shows each annual take-home cost at that same gross contribution. Its next row shows the normalized annual deposits under equal take-home cost—C in Traditional and the lower normalized Roth deposit. The final row shows those same-cost after-tax balances. Keeping the rows together prevents a common error: comparing a larger Roth deposit with a smaller-cost Traditional deposit while calling the investments equal.
Try a few retirement tax rates rather than trusting one forecast. If the direction changes only under a narrow assumption, that uncertainty itself is useful. If you expect a high-income pension or large taxable withdrawals, explore a higher future rate; if you expect lower taxable income or significant deductions, explore a lower rate. A blend of account types can provide withdrawal flexibility. Review plan fees and matching rules before changing a workplace contribution because an available match can be more consequential than the simplified tax-rate difference.
Sources and Further Planning
For current rules, review the IRS Roth comparison chart, retirement plan distributions and tax information, and required minimum distribution guidance. Your plan summary and administrator can clarify whether contributions are deductible, how matching works and which withdrawal rules apply. IRS materials and plan details can change; check the current tax year rather than relying on an old summary.
For related perspectives, compare your broader savings path with the 401(k) calculator, Roth IRA calculator and FIRE calculator. Each addresses a different planning question. A tax professional or fiduciary financial planner can help connect contribution elections with income, benefits, withdrawal sequencing and household goals.