Roth IRA Calculator

A Roth IRA is funded with after-tax dollars: you get no upfront tax deduction the year you contribute, but in exchange, qualified withdrawals in retirement, including all of the investment growth, are entirely free of federal income tax. That trade only pays off if the account has time to compound, which is why this calculator models growth on a monthly compounding basis across your full working career rather than a single lump-sum projection.

The annual contribution limit modeled here is $7,000, consistent with the current IRS limit under Internal Revenue Code Section 408A, with an additional $1,000 catch-up contribution available starting at age 50, bringing the effective limit to $8,000 for older savers, a scenario this calculator's built-in "Age 50+ Catch-Up" toggle applies directly. Eligibility to contribute to a Roth IRA at all phases out at higher modified adjusted gross income levels, a rule this calculator does not enforce since it assumes you are eligible to contribute the full amount you specify.

The calculator's core value proposition is the side-by-side comparison it draws between the Roth balance and an equivalent Traditional IRA balance taxed at your stated retirement tax bracket. Roth withdrawals are untaxed, and Traditional withdrawals are taxed as ordinary income when you take them out, so the same accumulated balance is worth strictly less in a Traditional account once you actually spend it. This calculator quantifies that gap directly as the "tax advantage" dollar figure, turning an abstract tax-policy distinction into a concrete number you can compare against your own contribution decisions.

Step 1: Convert to monthly compounding. Your time horizon in years is converted to months, your annual return to a monthly rate, and your annual contribution to a monthly contribution:

$$i_{\text{monthly}} = \frac{\text{Annual Return}}{12}, \qquad \text{Monthly Contribution} = \frac{\text{Annual Contribution}}{12}$$

Step 2: Compound monthly across the full horizon. Each month, interest is earned on the existing balance, then the monthly contribution is added:

$$\text{Balance}_{m} = \text{Balance}_{m-1} \times (1 + i_{\text{monthly}}) + \text{Monthly Contribution}$$

Step 3: Decompose growth versus contributions.

$$\text{Total Growth} = \text{Final Balance} - \text{Total Contributions (starting balance} + \text{annual contribution} \times \text{years)}$$

Step 4: Compare against an equivalent Traditional IRA. The final Roth balance is compared to what the same balance would be worth net of tax if withdrawn from a Traditional account at your stated retirement tax bracket:

$$\text{Traditional Net Value} = \text{Final Balance} \times (1 - \text{Retirement Tax Rate})$$ $$\text{Roth Tax Advantage} = \text{Final Balance} - \text{Traditional Net Value}$$

Using this calculator's baseline inputs: a 25-year-old with a $15,000 starting balance, contributing $7,000 annually, an 8.5% expected annual return, retiring at 65 (40 years of growth), with a 22% assumed retirement tax bracket.

1. Time horizon: 65 − 25 = 40 years = 480 months
2. Monthly rate: 8.5% ÷ 12 ≈ 0.7083%
3. Monthly contribution: $7,000 ÷ 12 ≈ $583.33
4. Compounding runs for 480 months, interest applied to the balance each month before that month's contribution is added.
5. Final Roth balance at age 65: $2,799,987.34
6. Total contributions over 40 years: $15,000 starting balance + ($7,000 × 40 years) = $15,000 + $280,000 = $295,000
7. Total tax-free growth earned: $2,799,987.34 − $295,000 = $2,504,987.34
8. Equivalent Traditional IRA net value (same balance, taxed at 22% on withdrawal): $2,799,987.34 × (1 − 0.22) = $2,183,990.12
9. Roth tax advantage: $2,799,987.34 − $2,183,990.12 = $615,997.21

That $615,997.21 figure is the calculator's headline insight. On identical contributions and identical growth, simply holding the money in a Roth instead of a Traditional account, and thus never owing tax on the $2,504,987.34 of growth, is worth over $615,000 more in spendable retirement dollars at a 22% tax rate. For a second reference point, this calculator's own test suite shows the pure compounding effect in isolation: a single $20,000 lump-sum contribution with zero future additions, growing at 8.0% monthly-compounded over 30 years, reaches $218,714.59, an 11-fold increase driven entirely by compound growth on the original contribution.

• Income eligibility phase-outs. Roth IRA contribution eligibility phases out above certain modified adjusted gross income thresholds; high earners may be ineligible to contribute directly and may need to use a "backdoor Roth" conversion strategy instead. This calculator assumes full eligibility.
• The apples-to-apples contribution comparison with Traditional accounts. This calculator compares equal dollar contributions to both account types. In reality, a Traditional IRA contribution reduces your current-year taxable income, meaning the same take-home pay allows for a larger pre-tax contribution than an equivalent after-tax Roth contribution; some analyses account for this by assuming the Traditional contributor invests their upfront tax savings separately.
• Early withdrawal penalties and ordering rules. Roth IRA contributions (though generally not earnings) can be withdrawn tax- and penalty-free at any time; this calculator does not model early withdrawal scenarios or the five-year holding period rule that applies separately to converted funds and to earnings.
• Required Minimum Distributions. Roth IRAs are not subject to RMDs during the original owner's lifetime, unlike Traditional IRAs; this calculator does not model any forced distribution schedule for either account type.
• Variable future tax rates. The comparison uses a single flat assumed retirement tax bracket; actual future tax rates depend on legislation, your total taxable income in retirement, and the tax bracket structure in effect decades from now, none of which can be known with certainty today.

• Assuming Roth and Traditional accounts always produce different total balances. If your tax rate is identical at contribution and at withdrawal, and contribution amounts are treated as directly equivalent, the pre-tax value of both accounts is mathematically the same; the Roth's advantage in this model comes specifically from comparing equal after-tax contribution amounts against a taxable withdrawal.
• Overlooking the $7,000 (or $8,000 with catch-up) annual contribution limit. Entering an annual contribution above the statutory limit produces a projection you cannot actually replicate under current IRS rules.
• Ignoring income phase-out limits. High earners who contribute directly to a Roth IRA despite exceeding the income limit can trigger excess contribution penalties; check current IRS income thresholds before assuming you are eligible.
• Using an unrealistically high or low return assumption. Equity-heavy portfolios have historically returned somewhere in the high single digits nominally over multi-decade periods with substantial year-to-year variance; test a range of return assumptions rather than relying on one point estimate.
• Forgetting that monthly compounding produces a higher effective annual yield than the stated annual rate. Because this calculator compounds monthly, the effective annual growth rate is slightly higher than the nominal annual return entered, an important distinction when comparing this projection against annually-compounded illustrations elsewhere.

• IRS Publication 590-A, Contributions to Individual Retirement Arrangements (IRAs), https://www.irs.gov/publications/p590a
• IRS Publication 590-B, Distributions from Individual Retirement Arrangements (IRAs), https://www.irs.gov/publications/p590b
• Internal Revenue Code Section 408A, Roth IRA statutory provisions.
• U.S. Securities and Exchange Commission, Investor.gov Roth IRA guide, https://www.investor.gov/introduction-investing/investing-basics/investment-products/roth-iras