The decision is one comparison
A traditional account gives you a tax deduction now and taxes withdrawals in retirement. A Roth gives no deduction now and tax-free withdrawals later. Everything else follows from that.
Which wins comes down to a single comparison: is your tax rate higher now or in retirement? If your retirement rate will be lower, traditional wins. If higher, Roth wins. If identical, they are mathematically equivalent — a fact that surprises people, but the arithmetic is symmetric.
With the defaults — 24% now, 22% later — the two land within about $3,000 of each other on balances near $660,000. That is well under 1%, which is the practically important result: for most people in the middle brackets, this decision matters far less than simply contributing.
The refund is where the comparison usually breaks
Contributing $7,000 to a traditional account at a 24% marginal rate saves $1,680 in tax that year. For the comparison to be fair, that $1,680 must be invested — otherwise you are comparing $7,000 of Roth contributions against $5,320 of real traditional cost, and the Roth appears better simply because you put in more.
This is why the calculator has a toggle for it. Invest the savings and the traditional account's side balance grows to roughly $142,000 after capital gains tax, closing nearly all the gap. Spend the refund and traditional falls behind significantly.
In practice, most people spend it. If you know you will not invest the difference, the Roth's forced-savings effect is a genuine advantage — not a mathematical one, but a behavioural one that shows up in real outcomes.
Reasons to favour Roth beyond the maths
Roth accounts have several structural advantages the headline comparison misses. Roth IRAs have no required minimum distributions during the owner's lifetime, so the money can keep compounding untouched, while traditional accounts force withdrawals in your seventies whether you need the money or not.
Roth contributions — though not earnings — can be withdrawn at any time without tax or penalty, which makes a Roth IRA a reasonable secondary emergency reserve.
Tax diversification matters too. Holding both types lets you manage your taxable income in retirement, drawing from traditional up to the top of a low bracket and from Roth beyond it. That flexibility has real value given nobody knows what future tax rates will be.
Roth also passes to heirs more cleanly, since they inherit tax-free rather than owing income tax on withdrawals.
Where each clearly wins
Roth is the stronger choice early in your career, when your income and marginal rate are at their lowest and you have decades of tax-free growth ahead. It is also the better option if you expect substantial retirement income from pensions or rental property, which may push you into a higher bracket than you occupy now.
Traditional is stronger during peak earning years, particularly in the 32% bracket and above, where the deduction is worth the most and retirement income is likely to be taxed at a lower rate. It also helps if a deduction reduces your income enough to qualify for other tax benefits.
A frequently overlooked strategy: use traditional during high-earning years, then convert to Roth during low-income years — an early retirement gap, a sabbatical, a career break — when the conversion is taxed at a low rate. This captures the deduction at a high rate and pays the tax at a low one.
Tax rules change and individual circumstances vary enormously. This is a place where a conversation with a tax professional often pays for itself.
Frequently asked questions
- Can I contribute to both?
- Yes, and many people should. Contribution limits are shared across account types, but splitting between them provides useful tax flexibility in retirement.
- What tax rate should I assume for retirement?
- Most people land somewhat below their peak working rate, since retirement income is usually lower and drawn partly from tax-free sources. Assuming the same rate is a reasonably conservative default.
- Does the employer match go into the Roth?
- Historically employer matches went into a traditional pre-tax account even for Roth 401(k) contributions, though recent rule changes allow plans to offer Roth matching. Check your plan documents.
- What is a backdoor Roth?
- A method for high earners above the Roth IRA income limits: contribute to a traditional IRA and convert it to a Roth. The pro-rata rule can create unexpected tax if you hold other pre-tax IRA balances, so it is worth professional advice.