Scope boundary: This article is education only. Monaco CPA may report tax treatment and applicable limits for client-established accounts within a written tax-return engagement, but does not select, recommend, establish, administer, manage, or invest retirement accounts; implement Backdoor Roth transactions; or provide defined-benefit or cash-balance plan services. Use an independent TPA, custodian, actuary, or financial adviser. Last updated: July 14, 2026.
In This Article
- What Retirement Plan Choice Do Most NJ Self-Employed People Get Wrong?
- What Are the 2026 Contribution Limits for NJ Self-Employed Retirement Plans?
- How Does a SEP-IRA Work for NJ Self-Employed Individuals?
- How Do Solo 401(k) Rules Compare for NJ Owner-Only Businesses?
- How Do SIMPLE IRA Rules Compare With 401(k) Rules?
- How Are Defined Benefit Plans Treated for NJ Tax Purposes?
- Why Does NJ's Non-Conformity on Retirement Deductions Matter So Much?
- What Does the SEP-IRA vs. Solo 401(k) Tax Difference Look Like in Real Numbers?
- Educational Comparison Factors
- Sources and References
- Frequently Asked Questions
- Written Tax-Return Scope for an Established Account
What NJ Self-Employed People Need to Know About Retirement Plans
When a self-employed person or S-corp owner asks what retirement plan to set up, the most common answer they get is: "Just open a SEP-IRA. It's simple."
That advice may be workable from a federal-tax standpoint, but NJ treatment must be separated by contribution type. Per N.J.S.A. 54A:6-21, employee 401(k) elective deferrals are excludable from NJ gross income; NJ guidance does not clearly address employer match or profit-sharing contributions to a Solo 401(k), so confirm that share for your facts. By contrast, New Jersey gross income tax rules (see NJ GIT-2) disallow NJ deductions for traditional IRA contributions, and SEP-IRA and SIMPLE IRA contributions create NJ basis rather than a current-year NJ exclusion. (Updated May 2026.)
The practical takeaway is to compare federal contribution limits, employee coverage rules, plan administration costs, Roth options, loan provisions, and NJ treatment. Do not assume the Solo 401(k) employer share produces a current NJ deduction; confirm that share for the taxpayer's facts. SEP-IRA contributions create NJ basis rather than a current-year NJ deduction.
This education-only guide compares 2026 contribution limits and NJ return treatment; Monaco CPA does not select, establish, administer, manage, or invest retirement accounts.
What Are the 2026 Contribution Limits for NJ Self-Employed Retirement Plans?
| Feature | SEP-IRA | Solo 401(k) | SIMPLE IRA | Defined Benefit (Cash Balance) |
|---|---|---|---|---|
| 2026 employee limit | N/A | $24,500 | $17,000 ($18,100 in plans subject to the higher §408(p)(2)(E) limit) | N/A |
| 2026 employer/total limit | $72,000 | $72,000 | 3% match or 2% non-elective (4%/3% enhanced election; optional extra non-elective up to 10% of pay, capped at $5,300) | Up to $290,000 §415(b) annual benefit |
| Catch-up (50+) | N/A | $8,000 | $4,000 | Actuarially determined |
| Enhanced catch-up (60–63) | N/A | $11,250 | $5,250 | N/A |
| Roth option | No | Yes | Yes (SECURE 2.0) | No |
| Loan provision | No | Yes (up to $50K) | No | Varies |
| Employees allowed | Yes | No (owner + spouse only) | Yes (must offer all) | Varies |
| Admin complexity | Very low | Low–medium | Low | High (actuary required) |
| Establishment deadline | Tax filing deadline | Employer contributions: filing deadline incl. extensions (SECURE sec. 201); employee deferral election: Dec 31 | October 1 | Filing deadline incl. extensions (SECURE sec. 201) |
| NJ deductibility | No (creates NJ basis) | Deferrals: Yes per N.J.S.A. 54A:6-21; employer share not clearly addressed - confirm for your facts | No (creates NJ basis) | No (creates NJ basis; 54A:6-21 covers only 401(k) plans) |
How Does a SEP-IRA Work for NJ Self-Employed Individuals?
A SEP-IRA (Simplified Employee Pension) is the simplest retirement plan for self-employed individuals. There are no annual filings, no contribution formulas to track, and minimal administrative burden.
How contributions work: You contribute as the employer. For a sole proprietor or working partner, a 25%-of-compensation plan rate works out to roughly 20% of adjusted net self-employment earnings after the deductible portion of self-employment tax and the contribution-rate adjustment, up to $72,000 for 2026. Do not multiply Schedule C profit by 25%; use the IRS Publication 560 worksheet. For a W-2 employee of your own S-corp, the limit is 25% of W-2 wages, up to $72,000.
The catch: SEP-IRA contributions are made on the employer side only. There's no employee deferral component. If you have employees, you must contribute the same percentage for all eligible employees. This is why many sole proprietors outgrow the SEP-IRA once they hire.
Federal tax benefit: The SEP-IRA contribution is deductible on Schedule 1 (Form 1040), reducing your federal AGI.
NJ tax benefit: None. New Jersey does not allow deductions for SEP-IRA contributions on the NJ-1040. Your NJ taxable income is unchanged by the SEP-IRA contribution. As a result, you will have a higher NJ basis in the account. Withdrawals in retirement that represent after-NJ-tax contributions are partially excluded from NJ income.
How Do Solo 401(k) Rules Compare for NJ Owner-Only Businesses?
The Solo 401(k) (also called individual 401(k) or self-employed 401(k)) is designed specifically for self-employed individuals and owners of businesses with no full-time employees other than the owner and spouse.
Two-part contribution structure:
- Employee deferral: Up to $24,500 for 2026 ($32,500 if age 50+, $35,750 if age 60-63 under SECURE 2.0 enhanced catch-up). This reduces your W-2 wages on Box 1 if you are an S-corp employee. Note: the indexed prior-year FICA-wage threshold for mandatory Roth catch-up treatment in 2026 is $150,000; plan coverage, age, wages from the sponsoring employer, and current transition rules still control. Year-specific figure reviewed August 2026.
- Employer profit-sharing: Up to 25% of your W-2 compensation (S-corp) or net SE income (sole prop), subject to the combined $72,000 annual limit.
Roth option: SECURE 2.0 Act expanded Roth availability for Solo 401(k)s. If your plan document allows it, you can make Roth employee deferrals, contributions from after-tax income that grow and are withdrawn tax-free.
Loan provision: Solo 401(k)s can allow loans of up to $50,000 or 50% of the vested balance, whichever is less. No SEP-IRA equivalent.
NJ treatment: Per N.J.S.A. 54A:6-21, employee elective deferrals (W-2 Box 12 Code D - allowed since 1984) are excludable from NJ gross income; NJ guidance does not clearly address Solo 401(k) employer profit-sharing or match contributions, so confirm that share for your facts. NJ Box 16 wages are reduced by the amount of pre-tax employee 401(k) deferrals. SEP-IRA and SIMPLE IRA contributions instead create NJ basis. (Updated May 2026.)
Establishment deadline: Under SECURE Act sec. 201, a Solo 401(k) can be adopted as late as your tax-filing deadline (including extensions) and treated as established on the last day of the prior year, so employer profit-sharing contributions can still be made for that year. December 31 remains the deadline for employee deferral elections (a sole proprietor's first plan year gets until the unextended filing deadline under SECURE 2.0 sec. 317).
How Do SIMPLE IRA Rules Compare With 401(k) Rules?
The SIMPLE IRA (Savings Incentive Match Plan for Employees) is designed for small businesses with up to 100 employees who want to offer employees a retirement benefit without the complexity of a full 401(k) plan.
Employee deferrals: Up to $17,000 for 2026 per IRS Notice 2025-67 (up from $16,500 in 2025). SIMPLE plans subject to the higher limit under IRC Section 408(p)(2)(E) use $18,100: the higher limit is automatic for employers with 25 or fewer employees and electable by employers with 26-100 employees that provide an enhanced 4% match or 3% non-elective contribution. Age-50 catch-up is $4,000 ($3,850 in higher-limit plans); the SECURE 2.0 enhanced catch-up for ages 60-63 is $5,250.
Employer obligation: You must either match employee deferrals up to 3% of compensation, OR make a flat 2% non-elective contribution for all eligible employees (even non-participants); an employer electing the higher-limit regime provides a 4% match or 3% non-elective contribution instead. The non-elective option applies to all eligible employees. You can't opt out. Employers may also permit an additional uniform non-elective contribution of up to 10% of compensation, capped at $5,300 for 2026 (Section 408(p)(2)(A)(iv), Notice 2025-67).
Roth option: SECURE 2.0 added a Roth option for SIMPLE IRAs, effective 2023.
Key limitation: If you withdraw from a SIMPLE IRA within 2 years of the first contribution, the early withdrawal penalty is 25% (not the usual 10%). This "2-year lock" makes SIMPLEs less flexible than 401(k)s for participants who may need early access.
NJ deductibility: Unlike 401(k) employee deferrals (which ARE excludable from NJ gross income per N.J.S.A. 54A:6-21), SIMPLE IRA employee deferrals are NOT excludable for NJ purposes. NJ Box 16 includes the deferred amount even though federal Box 1 is reduced. The deferrals create NJ basis recoverable tax-free in retirement under the 3-Year Rule or General Rule. Employer match/non-elective contributions to a SIMPLE IRA also create NJ basis rather than producing a current-year NJ deduction.
How Are Defined Benefit Plans Treated for NJ Tax Purposes?
Service boundary: Monaco CPA does not provide cash-balance or defined-benefit plan design or analysis; consult an independent actuary/TPA and plan adviser. A cash-balance or traditional defined-benefit plan can permit contributions beyond the $72,000 defined-contribution limit. The 2026 §415(b) annual benefit limit is $290,000 per IRS Notice 2025-67 (up from $280,000 in 2025); the required contribution is actuarially determined from the plan terms and participant facts. Suitability, funding obligations, and plan design require independent actuarial and fiduciary advice.
The defined-benefit promise specifies a projected benefit at retirement, and an actuary certifies the annual funding requirement. Qualifying contributions may be federally deductible, subject to the plan and taxpayer facts.
NJ treatment: Employer contributions to a defined-benefit plan are not excludable or deductible for NJ gross income tax purposes. They are taxable for NJ and create NJ basis recoverable in retirement; N.J.S.A. 54A:6-21 covers only 401(k) contributions.
The catch: Annual actuarial cost (~$1,500–$3,000/year) and minimum funding requirements. Once established, you are obligated to fund the plan at actuarially required levels.
Why Does NJ's Non-Conformity on Retirement Deductions Matter So Much?
This section explains a material federal-NJ treatment difference for retirement contributions.
New Jersey conforms to federal rules on what contributions can be made, but not to federal rules on deductibility. Specifically:
- NJ-1040 does not allow deductions for IRA contributions (neither traditional IRA nor SEP-IRA) under New Jersey gross income tax rules (see NJ GIT-2). This is explicitly stated in the NJ-1040 instructions at line 27a.
- NJ excludes employee 401(k) elective deferrals under N.J.S.A. 54A:6-21. NJ guidance does not clearly address the Solo 401(k) employer profit-sharing or match share, so confirm that share for the taxpayer's facts. Defined-benefit employer contributions are taxable for NJ and create NJ basis.
What this means in practice:
| Plan Type | Federal Tax Benefit | NJ Tax Benefit |
|---|---|---|
| SEP-IRA | Deductible (reduces AGI) | Not deductible on NJ-1040 |
| Traditional IRA | Deductible (income limits apply) | Not deductible on NJ-1040 (NJ gross income tax rules; see GIT-2) |
| Solo 401(k) employer contribution | Deductible (reduces business income) | Not clearly addressed by NJ guidance - confirm for your facts |
| Solo 401(k) employee deferral | Reduces W-2 Box 1 | Excludable from NJ gross income (W-2 Box 16 reduced; N.J.S.A. 54A:6-21) |
| SEP-IRA contribution | Deductible | NOT deductible on NJ return (creates NJ basis recoverable in retirement) |
| SIMPLE IRA employee deferral and employer match | Deductible | NOT deductible on NJ return (creates NJ basis) |
| Defined benefit plan employer contribution | Deductible | Taxable for NJ - no exclusion (54A:6-21 covers only 401(k) plans); creates NJ basis |
The accurate consequence: Per N.J.S.A. 54A:6-21, NJ allows a current-year exclusion for 401(k) employee elective deferrals - NJ gross income and NJ Box 16 wages are reduced. NJ guidance does not clearly address Solo 401(k) employer contributions, so confirm that share for your facts. Defined-benefit employer contributions are taxable for NJ because the 54A:6-21 exclusion covers only 401(k) plans. SEP-IRA, SIMPLE IRA, and traditional IRA contributions likewise are not excludable from NJ gross income and create NJ basis recoverable in retirement under the 3-Year Rule or General Rule. A neutral comparison depends on the complete contribution, coverage, administration, and tax facts; Monaco CPA does not make the plan-selection decision.
If a taxpayer funds a Solo 401(k) with $72,000, federal treatment must be computed from the employee-deferral and employer-share components. For NJ, the employee-deferral share clearly reduces NJ gross income, while the employer share must be confirmed for the taxpayer's facts. A $72,000 SEP-IRA contribution may reduce federal AGI but does not reduce NJ gross income in the contribution year; it creates NJ basis recoverable later. These differences are inputs to the plan comparison, not a recommendation by themselves. (Updated May 2026.)
What Does the SEP-IRA vs. Solo 401(k) Tax Difference Look Like in Real Numbers?
Illustrative scenario: NJ S-corp owner (single filer), $200,000 W-2 from the S-corp, and $200,000 of NJ taxable income before retirement contributions. Compare a $50,000 SEP-IRA employer contribution with a $50,000 Solo 401(k) package consisting of a $24,500 employee deferral and a $25,500 employer share. The illustration assumes a 24% federal rate and a 6.37% NJ marginal rate; it does not model QBI, payroll, plan costs, or other return items.
| Item | SEP-IRA ($50,000 employer) | Solo 401(k) ($24,500 employee + $25,500 employer) |
|---|---|---|
| Federal income reduction | $50,000 | $50,000 |
| Federal income-tax effect (24% simplifying assumption) | ~$12,000 | ~$12,000 |
| Clear NJ income reduction (current year) | $0 | $24,500 employee deferral |
| Clear NJ income-tax effect (6.37%) | $0 | $1,560.65 |
| Unresolved NJ component | N/A | $25,500 employer share - confirm for the taxpayer's facts |
| NJ basis | $50,000 | Depends on confirmed treatment of the employer share |
The $1,560.65 NJ figure is $24,500 × 6.37% and reflects only the clearly excludable employee deferral. No NJ saving is asserted for the Solo 401(k) employer share. The choice also depends on contribution limits, employee coverage, Roth and loan provisions, administration, QBI, payroll, and plan costs. Neither owner contribution is a Schedule C expense or reduces self-employment tax.
Educational Comparison Factors
- Employee-coverage and owner-only eligibility rules
- Compensation or self-employment income used by the contribution formula
- Adoption, election, contribution, and filing deadlines
- Plan-document provisions, including any Roth or loan feature
- Federal and NJ tax treatment, basis tracking, fees, and administration
- Independent TPA, custodian, actuary, fiduciary, and investment-advice requirements
Sources and References
- IRC §402 (Solo 401(k) deductibility)
- IRC §408 (IRA rules)
- IRC §219 (IRA deduction, federal)
- N.J.S.A. 54A:6-21 (NJ exclusion for 401(k) employee elective deferrals)
- NJ Division of Taxation Bulletin GIT-2 (NJ non-conformity with IRA deductions)
- NJ-1040 Instructions, Line 27a (IRA deduction. NJ)
- IRS Publication 560 (Retirement Plans for Small Business)
- SECURE 2.0 Act of 2022 (Pub. L. 117-328)
Scope boundary: Monaco CPA does not provide defined-benefit or cash-balance plan design or analysis. Consult an independent actuary/TPA and plan adviser for those plans.
Frequently Asked Questions
Can I contribute to both a Solo 401(k) and a SEP-IRA in the same year?
An employer may maintain a SEP and another qualified plan for the same business, but plan documents, elective-deferral coordination, and the combined IRC §415(c) limits must be applied. The simplified Form 5305-SEP generally cannot be used when the employer maintains another qualified plan unless that other plan is also a SEP; a prototype or individually designed SEP may be needed. Coordinate the plan documents and contribution limits before funding both.
What's the deadline to establish a Solo 401(k)?
Under SECURE Act sec. 201, a Solo 401(k) can be adopted as late as your tax-filing deadline (including extensions) for the prior year and treated as established on December 31 - so you can open a plan in 2027 and make 2026 employer profit-sharing contributions. December 31 still matters for employee deferrals: elections must generally be in place by year-end (S-corp owners defer through payroll during the year), except that under SECURE 2.0 sec. 317 a sole proprietor may make first-plan-year employee deferrals up to the unextended filing deadline.
Why does NJ not allow IRA deductions?
New Jersey's income tax was designed with its own set of deductions that don't mirror federal law. Under New Jersey gross income tax rules (see NJ GIT-2), NJ specifically excludes IRA deductions. The silver lining: because you don't get a NJ deduction when you contribute, your after-NJ-tax basis in the IRA is higher. When you withdraw in retirement, the basis is excluded from NJ income tax under the NJ IRA exclusion rules.
I have a SEP-IRA already set up. Should I switch to a Solo 401(k)?
A switch is not implied by this comparison. Existing SEP-IRA funds may remain in place or may be eligible for rollover if the receiving plan permits it, but plan documents, deadlines, contribution coordination, fees, investments, and federal and NJ treatment must be reviewed. Use an independent TPA, custodian, and financial adviser for selection, establishment, rollover, administration, and investments.
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