For most people, splitting your 401(k) between Roth and traditional is the smart default, because nobody can predict what tax rates or their own income will look like decades from now. The two sides are taxed at opposite ends of the timeline, and funding both gives you tax-free money and tax-deferred money to draw from in retirement. The combined limit for both types in 2026 is $24,500, and every dollar you put into one side reduces what you can put into the other.1Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 The right ratio depends on where your income sits today, where you think it will sit in retirement, and how much of that prediction you actually trust.
How the Two Sides Are Taxed
Traditional 401(k) contributions come out of your paycheck before federal income tax is calculated, so they reduce your taxable income for the year.2Internal Revenue Service. 401(k) Plan Overview Earn $90,000, defer $10,000 to traditional, and the IRS treats you as though you earned $80,000 for income tax purposes. The money grows tax-deferred, and you pay ordinary income tax on every dollar you withdraw in retirement. Traditional contributions still get hit with Social Security and Medicare taxes in the year you earn them; the payroll tax break only touches federal income tax withholding.3Internal Revenue Service. Are Retirement Plan Contributions Subject to Withholding for FICA, Medicare, or Federal Income Tax
Roth 401(k) contributions work the opposite way. You pay full income tax on the money before it goes in, so there is no deduction now.4Office of the Law Revision Counsel. 26 U.S.C. 402A – Optional Treatment of Elective Deferrals as Roth Contributions In exchange, qualified withdrawals in retirement come out completely tax-free, growth included. A distribution qualifies as tax-free when it happens at least five years after your first Roth 401(k) contribution and after you reach age 59½.5Internal Revenue Service. Roth Account in Your Retirement Plan
When you split, you are building two pools with different tax characteristics. One will be taxed later at whatever rates apply. The other has already been taxed and will never be taxed again.
When Roth Makes More Sense
The math is straightforward. If your tax rate today is lower than your tax rate in retirement, Roth wins: you pay the cheaper rate now and withdraw tax-free later. Several situations tilt the scale that way:
- Early-career or lower-income years, when your taxable income falls in the 12% or 22% federal bracket. Paying 12% now to avoid 22% or 24% later is a good trade.
- A long time horizon. A 30-year-old contributing to Roth gets 30-plus years of tax-free growth, and the longer the runway, the more valuable the tax-free compounding.
- Expecting higher future income from promotions, a career change, or a spouse returning to work.
- Concern about future tax policy. Federal rates have changed many times; every dollar in a Roth is insulated from that risk.
There is a subtlety worth knowing. Because Roth contributions are made with after-tax dollars, a $24,500 Roth contribution is effectively worth more than a $24,500 traditional contribution. The traditional money still owes tax on the way out, so its real purchasing power is lower even when the balance looks identical.
When Traditional Makes More Sense
If your current tax rate is higher than what you expect to pay in retirement, the traditional side wins. You dodge the expensive rate today and pay the cheaper rate later.
- Peak earning years in the 32% or 35% bracket. A $24,500 traditional deferral at 32% saves $7,840 in federal taxes for the year.
- Planning to spend less in retirement than you earn now. Lower spending means lower withdrawals, which usually means a lower bracket.
- Being close to retirement. With fewer years of tax-free growth ahead, the Roth’s compounding advantage shrinks and the immediate deduction matters more.
- Living in a high-income-tax state now and planning to retire somewhere with no state income tax. Traditional lets you deduct at the higher state rate and withdraw at zero.
Why a Split Is the Sensible Default
Here is the honest truth: nobody knows what tax rates will look like in 20 or 30 years, and most people cannot predict their own retirement income within a bracket either. Splitting is an admission of that uncertainty. Funding both sides guarantees that some of your retirement income will be tax-free no matter what Congress does, and it lets you choose year by year in retirement which account to draw from to manage your taxable income.
There is also a bracket-straddling move worth knowing. Say your taxable income is $95,000 and the 22% bracket ends at $103,350 for single filers. You could put enough into traditional to bring your taxable income down to the top of the 12% bracket ($48,475 for single filers in 2025), then send the rest of your contribution to Roth. Every traditional dollar saves 22 cents in tax, and every Roth dollar locks in today’s rates for tax-free growth.
If you truly cannot say whether your retirement rate will be higher or lower, a 50/50 split is a reasonable starting point. Adjust it annually as your income and timeline change.
The 2026 Contribution Cap Applies to Both Combined
Traditional and Roth share a single annual cap. For 2026, the combined elective deferral limit is $24,500.1Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 Put $15,000 into traditional and you can put no more than $9,500 into Roth. The limit is per person, not per plan, so if you contribute to two employers’ plans during the year, the $24,500 ceiling applies across both.
Workers 50 and older can make additional catch-up contributions of $8,000, for a total deferral of up to $32,500. Workers aged 60 through 63 have access to a larger catch-up of up to $11,250, for a possible total deferral of $35,750, if their plan specifically allows it.1Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 Catch-up dollars split between traditional and Roth the same way regular contributions do.
Required Minimum Distributions Now Favor Roth
Traditional 401(k) accounts are subject to required minimum distributions starting at age 73. Those mandatory withdrawals count as taxable income and can push you into a higher bracket or trigger additional tax on Social Security benefits.
Roth 401(k) accounts used to carry the same requirement, but SECURE 2.0 eliminated RMDs for Roth accounts in employer plans starting in 2024.6Internal Revenue Service. Retirement Plans FAQs on Designated Roth Accounts That is a real planning advantage. Money in your Roth 401(k) can sit and grow tax-free for as long as you live, which makes it a useful wealth-transfer tool if you do not need the money yourself. This change alone strengthens the case for directing some contributions to the Roth side.
Early Withdrawals From the Roth Side Are Less Flexible Than People Expect
If you need to pull money out before 59½, the Roth 401(k) has a quirk that catches people off guard. Unlike a Roth IRA, where you can withdraw your own contributions tax-free at any time before touching earnings, a non-qualified Roth 401(k) distribution is split proportionally between contributions and earnings. You will owe income tax on the earnings portion plus a 10% early withdrawal penalty on that taxable amount.7Internal Revenue Service. Retirement Topics – Designated Roth Account
If your Roth 401(k) holds $50,000 in contributions and $10,000 in earnings, an early withdrawal of $6,000 will not come entirely from contributions. Roughly one-sixth of the account is earnings, so about $1,000 of that $6,000 would be taxable. If there is any real chance you will need the money before 59½, factor that into how heavily you lean Roth.
Setting the Split Up
Most plan administrators let you change your contribution election through an online portal. Look for a tab labeled something like “contributions” or “elections.” You will typically see two input fields, one for pre-tax and one for Roth, and you enter either a percentage of gross pay or a flat dollar amount in each.
For a 60/40 traditional-to-Roth split on a 10% total contribution rate, you would enter 6% in the pre-tax field and 4% in the Roth field. Changes usually take effect within one to two pay cycles. After your first paycheck under the new election, check that two separate line items appear on your pay stub, generally labeled something like “401k Pre-Tax” and “401k Roth,” with the correct amounts. If the numbers do not match what you elected, contact payroll before the next pay period. Keep the confirmation from your election change with your financial records.