Roth IRA Calculator — pay tax now, never again

A Roth IRA calculator answers one central question: how much tax-free income can your after-tax contributions realistically build by the time you retire? Because a Roth flips the usual tax order — you pay the IRS today instead of later — the payoff shows up decades down the road, and it's easy to underestimate just how large that payoff can be.

At Arb Digital we get asked constantly why Roth accounts get so much attention from financial writers. This calculator exists to make the answer concrete: put in your numbers, and watch exactly how much of your future balance the IRS will never be able to touch.

What This Roth IRA Calculator Does

You enter your current age, target retirement age, existing Roth balance, planned annual contribution, and expected return. The calculator compounds your after-tax contributions year over year and shows the resulting balance — every dollar of which is yours to withdraw tax-free in retirement, assuming you meet the standard holding and age requirements. It also estimates what you're saving in future taxes compared with a similar taxable brokerage account, and shows the "equivalent pre-tax value" your balance represents if you were instead comparing it to a Traditional account.

That last figure is worth pausing on. Because a Roth balance is already after-tax, it isn't directly comparable dollar-for-dollar to a pre-tax Traditional balance. The "equivalent pre-tax value" divides your Roth balance by one minus your expected retirement tax rate, showing what a Traditional account would need to grow to in order to hand you the same spendable amount after tax. It's a quick way to see that a smaller Roth balance can actually represent more real purchasing power than a larger-looking Traditional balance once taxes are factored in.

A Simple Example

Consider a 30-year-old contributing $7,000 a year at a 7% expected return, with no existing balance, retiring at 65. That's 35 years of compounding, and because none of the growth is ever taxed, the entire projected balance is spendable income in retirement. Compare that with the same contribution pattern in a taxable brokerage account, where annual dividends and eventual capital gains taxes would chip away at the compounding along the way. The gap between the two outcomes is the real-dollar value of the Roth's tax-free structure — and it's usually far larger than people expect once multiple decades are involved.

How to Use the Roth IRA Calculator

1. Enter your current age and the age you plan to retire. The gap between them is how many years your contributions get to compound.
2. Enter your current Roth IRA balance, if you already have one open, or leave it at zero if you're starting fresh.
3. Enter your planned annual contribution. The 2025 limit is $7,000, or $8,000 if you're 50 or older.
4. Enter your expected annual return. A diversified stock-and-bond portfolio is often modeled around 6–8% long term.
5. Enter your current tax rate and your expected retirement tax rate, then click Calculate to see your tax-free balance and how much tax you avoided.

The Formula / How It's Calculated

Because Roth contributions are made with money you've already paid tax on, the calculator simply compounds your annual contribution at your expected return for each year until retirement — no tax drag is applied to the growth, since qualified Roth withdrawals are tax-free under current law. This mirrors the rules published by the IRS on Roth IRAs. The "tax saved" figure estimates what you would have owed on that same growth if it had instead accumulated in a fully taxable account and been taxed at your expected retirement rate.

Why Paying Tax Now Can Be the Better Deal

A Roth IRA locks in your tax rate today, on a relatively small contribution, in exchange for tax-free growth on what could become a much larger balance decades from now. This tends to work best for people who are young or currently in a lower tax bracket than they expect to be in later — for example, early-career earners, or anyone who expects tax rates in general to rise before they retire. The logic is simple: pay a modest tax bill on $7,000 now rather than an unknown, possibly larger tax bill on a much bigger balance in 30 years.

Compare that with a Traditional IRA, where you get the deduction today but owe ordinary income tax on every withdrawal later — including all the growth. If you expect your tax rate to be about the same or higher in retirement, a Roth usually comes out ahead.

The Income Phase-Out and the Backdoor Workaround

Not everyone can contribute directly to a Roth IRA. For 2025, the ability to contribute phases out for single filers with modified adjusted gross income between roughly $150,000 and $165,000, and for married couples filing jointly between roughly $236,000 and $246,000. Above those ranges, direct contributions aren't allowed. High earners often use a "backdoor Roth" strategy instead — contributing to a nondeductible Traditional IRA and then converting it to a Roth — though this involves tax rules worth reviewing with a professional, particularly if you hold other pre-tax IRA balances.

Contributions Can Come Out Any Time, Penalty-Free

One underappreciated Roth feature: because your contributions were already taxed, you can withdraw the amount you contributed (not the earnings) at any age, for any reason, without tax or penalty. This makes a Roth IRA unusually flexible compared with most other retirement accounts, though pulling contributions out early obviously reduces the amount left to compound toward retirement — something worth weighing carefully before treating it as a backup emergency fund.

This flexibility is one reason some people use a Roth IRA as a hybrid savings vehicle — building an emergency cushion inside the same account that's also working toward retirement, since the contributed principal is always accessible. The tradeoff is opportunity cost: every dollar pulled out early is a dollar that stops compounding tax-free for decades. Most planners still recommend keeping a separate cash emergency fund and letting the Roth run untouched, but it's genuinely useful to know the option exists if a real emergency arises.

Roth IRA vs. Roth 401(k)

A Roth IRA and a Roth 401(k) share the same core tax treatment — after-tax contributions, tax-free qualified withdrawals — but differ in important ways. A Roth IRA has the income phase-out described above and a lower annual contribution limit, but offers more investment choice since it's opened with a brokerage of your choosing. A Roth 401(k), offered through an employer plan, has no income limit at all and allows the same much higher contribution ceiling as a traditional 401(k), though investment options are limited to whatever the plan offers. Some savers use both: maxing an employer Roth 401(k) match first, then funding a Roth IRA separately for more investment flexibility, income permitting.

Why Starting Early Matters So Much for a Roth

Because Roth growth is never taxed, time is the single biggest lever you control. A dollar contributed at age 25 has decades longer to compound tax-free than the same dollar contributed at 45, and the difference isn't linear — it accelerates in the later years as the balance itself grows larger. This is part of why young earners, even in modest first jobs, are often steered toward a Roth IRA over a Traditional one: the tax rate they lock in today tends to be low, and the runway ahead of them is long. Use this calculator to compare starting at different ages with the same contribution amount, and the gap tends to be far larger than most people expect.

Common Mistakes to Avoid

• Contributing above the income limit. Excess contributions can trigger a 6% excise tax each year they remain in the account until corrected.
• Assuming your tax rate in retirement will definitely be lower. Many retirees are surprised to find their effective rate similar to, or higher than, their working years once required withdrawals and Social Security are combined.
• Withdrawing earnings early. Unlike contributions, earnings withdrawn before age 59½ (and before the account is 5 years old) can trigger both tax and a 10% penalty.
• Ignoring the five-year rule. Each Roth conversion has its own five-year clock for penalty-free withdrawal of converted amounts.
• Forgetting employer plan Roth options. A Roth 401(k) has no income limit and a much higher contribution cap — worth comparing if your employer offers one.

Related Free Tools From Arb Digital

Compare this projection with the Traditional IRA Calculator to see the pre-tax alternative, or model your workplace plan with the 401k Calculator. If you already have pre-tax savings, our Roth Conversion Calculator shows what converting could cost and save. You can also check the broader picture with the Retirement Calculator, or browse everything on the free online tools hub.

Frequently Asked Questions

This tool provides general estimates for educational purposes only and is not financial, tax, legal, or medical advice. Figures are illustrative; consult a licensed professional for decisions.