A SEP IRA and a Solo 401(k) both allow considerably higher contributions than a standard IRA, which is exactly why business owners reach for them. What gets left out of that conversation is that both plans still have a hard ceiling, set by the same overall IRS rule regardless of which plan you use, and that every dollar inside either one is locked into doing exactly one job until you retire.
The Ceiling Still Exists, It Is Just Higher
Both SEP IRAs and Solo 401(k) profit-sharing contributions are ultimately capped by the same overall annual limit under IRC Section 415, the rule that governs total combined contributions across employer sponsored retirement plans. A business owner cannot get around this ceiling by stacking a SEP IRA on top of a Solo 401(k) profit-sharing contribution from the same business income; the combined total is still bound by the same overall limit. Higher than a standard IRA, yes. Unlimited, no.
Why the Formula Matters as Much as the Ceiling
A SEP IRA contribution is calculated purely as a percentage of compensation, which means a business owner with a modest net compensation figure, even with strong revenue, can find their maximum SEP contribution surprisingly low relative to what they actually have available to save. A Solo 401(k) generally allows a separate employee deferral on top of the employer contribution, which often permits meaningfully more total savings at moderate income levels, but both plans converge toward the same overall ceiling as income rises.
The Bigger Limitation: A Dollar That Can Only Do One Job
Here is the limitation that gets far less attention than the contribution ceiling itself. A dollar contributed to a SEP IRA or Solo 401(k) is locked into a single purpose: growing for retirement, inaccessible without penalty before a specific age, and in the case of a SEP IRA specifically, generally unavailable as a loan under any circumstance. A Solo 401(k) may permit a loan under specific plan provisions, but that loan reduces the amount actively invested and growing inside the account while it is outstanding, and must be repaid on a defined schedule or risk being treated as a taxable distribution.
Compare this to the family bank and infinite banking strategies covered earlier in this series. A dollar directed into a properly designed participating whole life or IUL policy can do more than one job at the same time. It continues growing inside the policy while simultaneously being available to borrow against for a business opportunity, an equipment purchase, or an unexpected need, without the same early withdrawal penalties or rigid loan restrictions that qualified plans impose. The retirement account dollar sits and waits. The properly structured policy dollar can work, and be recycled, while still building toward the original goal.
Why This Matters Specifically for Business Owners
Business owners, more than almost any other group, regularly need access to capital for opportunities that show up on their own timeline, not on a schedule set by IRS retirement rules. A dollar trapped inside a SEP IRA cannot help fund a piece of equipment, cover a slow season, or capitalize on a sudden opportunity without triggering taxes and penalties if accessed before retirement age. This is exactly the gap that a properly designed family bank strategy is built to fill, working alongside qualified retirement accounts, not replacing them.
Why the Right Answer Is Usually Both, Not Either
This is not an argument against SEP IRAs or Solo 401(k) plans. Fully using available qualified plan contribution room generally remains a strong first step, particularly given the upfront deduction available. It is an argument for recognizing exactly where that plan's ceiling sits, and what its dollars can and cannot do for you while they wait for retirement, so you can build the rest of your strategy around those specific limitations rather than assuming the retirement plan alone is a complete answer.
If you already have a CPA, this is a great, concrete conversation to bring to them directly. If you do not, we work with tax professionals across all fifty states and are glad to make an introduction.
Your Next Step
Our Wealth Blueprint Guide includes a full breakdown of exactly where the SEP IRA and Solo 401(k) ceilings sit, and what a family bank strategy alongside either plan could look like for your specific business.
Download the free Wealth Blueprint Guide and see exactly where your retirement plan ceiling sits, and what to do about it.
Get the Guide