Roth vs Traditional IRA Calculator

How This Roth vs Traditional IRA Calculator Works

The calculator treats your input as a pre-tax contribution budget – the amount of income you are prepared to set aside each year for retirement. It then adjusts that amount differently for Roth and Traditional scenarios.

• Roth scenario: You must first pay your current marginal tax rate on that income. Only the after-tax dollars go into the Roth IRA, but they then grow and can typically be withdrawn tax-free in retirement.
• Traditional scenario: You contribute the full pre-tax amount to a Traditional IRA. You get the tax benefit now or a deduction today, but withdrawals in retirement are taxed at your expected retirement tax rate.

The calculator assumes that you make the same contribution amount every year, that the money compounds at a constant annual rate of return, and that taxes are applied either up front for Roth or at the end for Traditional, but not in between. This gives you a clean, apples-to-apples comparison of how tax timing interacts with growth.

Core Formulas

Both IRA balances are modeled using the future value of an ordinary annuity, which assumes level contributions at the end of each year. The future value before any retirement taxes is:

Where:

• P = annual contribution actually deposited in the account
• r = annual rate of return as a decimal, so 7% = 0.07
• n = number of years you contribute and invest

The calculator uses this formula twice, once for Roth and once for Traditional, with different effective contributions.

Roth IRA Calculation

Let C be your annual pre-tax contribution budget and t_now be your current marginal tax rate as a decimal. Because Roth contributions are made with after-tax dollars, the amount that actually lands in the Roth account each year is:

PRoth = C × (1 − tnow)

The future value of the Roth account at retirement is then:

FVRoth = PRoth × ((1 + r)n − 1) / r

Under standard rules for qualified withdrawals, this Roth future value is already after-tax, because income tax was paid before the money entered the account.

Traditional IRA Calculation

For the Traditional IRA, your entire pre-tax budget is contributed:

PTrad = C

The pre-tax future value is:

FVTrad, pre-tax = PTrad × ((1 + r)n − 1) / r

Let t_ret be your expected retirement marginal tax rate. To estimate the spendable value after tax in retirement, the calculator multiplies by (1 − t_ret):

In simpler text form:

FVTrad, after = FVTrad, pre-tax × (1 − tret)

One subtle but important insight falls out of these formulas. When you compare the same pre-tax saving budget and assume the same growth rate and contribution schedule, the relative winner is driven mainly by the relationship between your current and future tax rates. Return and time still change the size of the balances, but the tax-rate comparison often decides which account type comes out ahead. That is why so much of the practical discussion around Roth versus Traditional centers on whether you expect your tax rate in retirement to be higher, lower, or about the same.

Interpreting Your Results

After you enter your assumptions and run the calculator, you will see two key numbers: the after-tax Roth balance and the after-tax Traditional balance at the end of your investment horizon. Here is how to read them:

• If the Roth after-tax value is higher, then under your assumptions it is more advantageous to pay tax now and enjoy tax-free withdrawals later.
• If the Traditional after-tax value is higher, then under your assumptions it is more advantageous to take the tax benefit today and pay tax at a lower rate in retirement.
• If the values are very close, then small changes in your future tax rate, returns, or contribution pattern could flip the result. In that case, the choice may hinge on flexibility, withdrawal rules, or your preference for tax diversification.

The most important driver in the comparison is the difference between your current and retirement tax rates:

• Higher tax rate now than in retirement: A Traditional IRA is often favored, because you avoid paying a high rate today and pay a lower rate later.
• Lower tax rate now than in retirement: A Roth IRA often looks better, since you lock in the lower tax rate today and avoid higher taxes later.

The rate of return and years to invest affect how much your money grows but, given the same pre-tax contribution budget and flat tax rates, they influence both accounts similarly. Where they matter most is in amplifying the consequences of getting the tax-rate assumption right or wrong. A long horizon makes a good tax decision matter over more dollars. A short horizon can make the difference smaller, but it does not change the basic logic of paying tax now versus later.

Worked Example

Suppose you enter the following values:

• Annual contribution pre-tax C = $6,000
• Current tax rate t_now = 24% or 0.24
• Retirement tax rate t_ret = 22% or 0.22
• Annual return rate r = 7% or 0.07
• Years to invest n = 30

Roth Scenario

After-tax contribution each year:

PRoth = 6,000 × (1 − 0.24) = 6,000 × 0.76 = 4,560

Future value:

FVRoth = 4,560 × ((1.07)30 − 1) / 0.07

Numerically, ((1.07)³⁰ − 1) / 0.07 is about 94.46, so:

FVRoth ≈ 4,560 × 94.46 ≈ $430,700 rounded

Because this is a Roth IRA, we treat the $430,700 as fully spendable in retirement under current qualified withdrawal rules.

Traditional Scenario

Annual contribution:

PTrad = 6,000

Future value before tax:

FVTrad, pre-tax = 6,000 × ((1.07)30 − 1) / 0.07

Using the same factor of about 94.46:

FVTrad, pre-tax ≈ 6,000 × 94.46 ≈ $566,800 rounded

After applying the retirement tax rate of 22%:

FVTrad, after = 566,800 × (1 − 0.22) = 566,800 × 0.78 ≈ $442,100

In this scenario, the Traditional IRA yields an estimated $442,100 after tax, slightly more than the Roth value of $430,700. That result reflects the assumption that your tax rate in retirement is lower than it is today. If you instead assumed a higher retirement tax rate, the Roth result would often come out ahead. The worked example also shows why looking only at the gross Traditional balance can be misleading. The pre-tax Traditional account looks much larger before taxes are applied, but the fair comparison is the amount you can actually spend.

When Roth vs Traditional IRA May Be Better

The calculator focuses on after-tax value, but qualitative factors also matter. The table below summarizes common situations in which one account type might be more attractive than the other, assuming the same pre-tax cost to you.

In practice, many savers use both account types across their careers to build tax flexibility in retirement. That approach can reduce the risk of guessing wrong about future tax law or future income. This calculator does not tell you that one account is universally superior. It helps you see how different assumptions tilt the math, so you can decide whether a pure Roth strategy, a pure Traditional strategy, or a blended approach fits your situation best.

Key Assumptions and Limitations

To keep the comparison transparent and easy to interpret, this tool makes several simplifying assumptions. These are important for understanding what the results do not cover.

• Constant tax rates: The calculator assumes your current and retirement tax rates remain fixed at the percentages you enter. In reality, tax brackets can change due to legislation, inflation adjustments, or shifts in your income.
• Single marginal rate: It models tax impact using a single marginal rate, not a full graduated tax bracket system.
• Constant annual return: Investment returns are assumed to be the same every year. Real markets fluctuate, and sequence-of-returns risk is not modeled.
• End-of-year contributions: Contributions are treated as if made at the end of each year. Contributing more frequently or earlier in the year would slightly change the actual growth.
• No IRS contribution limits: The tool does not enforce annual IRA contribution limits or income-based eligibility rules. In reality, your ability to contribute may be capped or restricted.
• No penalties or special rules: Early-withdrawal penalties, exceptions, and the five-year rules for Roth IRAs are ignored.
• No state or local taxes: Only a single combined tax rate is modeled. State and local income taxes, along with other levies, are not separately accounted for.
• Required minimum distributions: The complexities of RMDs for Traditional IRAs and the absence of lifetime RMDs for Roth IRAs under current rules are not modeled explicitly.
• Inflation not modeled separately: The calculator uses nominal dollar amounts and nominal rates of return. It does not adjust for purchasing power.
• No interaction with other accounts: Employer plans like 401(k)s, SIMPLE IRAs, pensions, and Social Security are not integrated into the projection.

Because of these limitations, the outputs should be viewed as illustrative estimates rather than precise forecasts. They are most useful when you compare scenarios. For example, you might enter one retirement tax rate, then rerun the numbers with a higher or lower rate to see how sensitive the answer is. That habit is often more valuable than treating one single output as definitive.

This calculator and explanation are for educational purposes only and do not constitute tax, legal, or investment advice. Individual situations vary, and tax laws change. Before making decisions about IRA contributions, conversions, or withdrawals, consider speaking with a qualified financial or tax professional who can evaluate your specific circumstances.