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 15, 2026.
In This Article
- How Does NJ Treatment Differ Across Self-Employed Retirement Plans?
- 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
How Does NJ Treatment Differ Across Self-Employed Retirement Plans?
SEP-IRA, Solo 401(k), SIMPLE IRA, and other plan types use different eligibility, contribution, employee-coverage, administration, and federal-versus-NJ rules. No plan label determines suitability.
Federal and New Jersey 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 resolves the employer share affirmatively: NJ-BUS-1 instructs the self-employed to deduct qualified Solo 401(k) contributions up to the federal limits, and employer contributions to qualified plans receive tax-deferred treatment under NJ wage guidance (amounts above the federal limits are not deductible for NJ). 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. The Solo 401(k) employer share is deductible per NJ-BUS-1 up to the federal limits; the residual checks are plan qualification and the federal-limit cap. 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 | Yes, if the SEP arrangement/provider supports designated Roth SEP contributions (SECURE 2.0; Notice 2024-2) | Yes | Yes (SECURE 2.0) | No |
| Loan provision | No | Yes (up to $50K; optional $10K floor) | 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: Yes per NJ-BUS-1 up to the federal limits (excess amounts not NJ-deductible) | No (creates NJ basis) | Employer contribution is tax-deferred for NJ - not currently taxable wages and creates no NJ basis; taxed when distributed |
How Does a SEP-IRA Work for NJ Self-Employed Individuals?
A SEP-IRA (Simplified Employee Pension) is an employer-funded retirement arrangement often used by self-employed individuals. It generally does not require the employer to file an annual Form 5500, but eligibility, uniform-contribution, calculation, and administration rules still apply.
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.
Employee-coverage rule: SEP-IRA contributions are employer contributions; there is no employee-deferral component. If the business has eligible employees, the employer generally must contribute the same percentage for each eligible participant. Apply the eligibility and contribution rules to the actual workforce before comparing plans.
Federal tax treatment: An eligible self-employed owner's SEP contribution generally is deducted on Schedule 1 (Form 1040), while an eligible S-corporation employer contribution is claimed by the corporation under the applicable return rules. Limits and timing depend on the contributor and plan facts.
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); for a sole proprietor or partner the Pub. 560 reduced-rate worksheet applies - a 25% plan rate works out to roughly 20% of adjusted net self-employment earnings - subject to the combined $72,000 annual limit.
Roth option: SECURE 2.0 expanded Roth availability for Solo 401(k)s. If the plan document allows it, Roth employee deferrals are made after tax; earnings and distributions receive Roth treatment only under the applicable qualification and distribution rules.
Loan provision: Solo 401(k)s can allow loans of up to the lesser of $50,000 or 50% of the vested balance - and a plan MAY permit borrowing up to $10,000 even when 50% of the vested balance is below $10,000 (IRC §72(p)(2)(A); the plan document controls whether loans, and that floor, are offered). 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 resolves the employer share affirmatively: NJ-BUS-1 instructs the self-employed to deduct qualified Solo 401(k) contributions up to the federal limits, and employer contributions to qualified plans receive tax-deferred treatment under NJ wage guidance (amounts above the federal limits are not deductible for NJ). 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 that want to offer a retirement benefit without the complexity of a full 401(k) plan. The employer generally may have no more than 100 employees who received at least $5,000 of compensation in the preceding year, counted across controlled or affiliated groups and subject to grace-period rules, and generally cannot maintain another retirement plan for the same year.
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 using NJ's IRA Worksheet C (see GIT-1&2; the Three-Year Rule and General Rule apply to contributory pensions and annuities other than IRAs). 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 is limited to the LESSER of 100% of the participant's highest-three-year average compensation or the $290,000 dollar ceiling per IRS Notice 2025-67 (up from $280,000 in 2025), with age/service adjustments; 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 receive tax-deferred treatment for New Jersey and are not currently taxable wages. They do not create NJ basis - NJ basis is limited to contributions you have already paid NJ tax on. The employer-funded portion and its untaxed earnings are taxable when distributed.
Ongoing obligations: Actuarial, administration, and funding requirements depend on the plan design, participant facts, provider scope, and actual quotes. Once established, the plan must be funded at the actuarially required levels under the applicable rules.
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 resolves the employer share affirmatively: NJ-BUS-1 instructs the self-employed to deduct qualified Solo 401(k) contributions up to the federal limits, and employer contributions to qualified plans receive tax-deferred treatment under NJ wage guidance (amounts above the federal limits are not deductible for NJ). Defined-benefit employer contributions receive tax-deferred treatment for NJ and are not currently taxable wages; they create no NJ basis and are taxed when distributed.
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) | Deductible per NJ-BUS-1 up to the federal limits; amounts above the federal limits are not deductible for NJ |
| 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) |
| SIMPLE IRA employee deferral and employer match | Deductible | NOT deductible on NJ return (creates NJ basis) |
| Defined benefit plan employer contribution | Deductible | Tax-deferred for NJ; not currently taxable wages and creates no NJ basis; taxed when distributed |
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 resolves the employer share affirmatively: NJ-BUS-1 instructs the self-employed to deduct qualified Solo 401(k) contributions up to the federal limits, and employer contributions to qualified plans receive tax-deferred treatment under NJ wage guidance (amounts above the federal limits are not deductible for NJ). Defined-benefit employer contributions receive tax-deferred treatment for NJ, are not currently taxable wages, create no NJ basis, and are taxed when distributed. SEP-IRA, SIMPLE IRA, and traditional IRA contributions likewise are not excludable from NJ gross income and create NJ basis recoverable in retirement using NJ's IRA Worksheet C (see GIT-1&2; the Three-Year Rule and General Rule apply to contributory pensions and annuities other than IRAs). 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 reduces NJ gross income, and the employer share is likewise deductible per NJ-BUS-1 up to the federal limits; the residual checks are plan qualification and the federal-limit cap. 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 |
| NJ income reduction (current year) | $0 | $50,000 - the $24,500 employee deferral (N.J.S.A. 54A:6-21) plus the $25,500 employer share, deductible per NJ-BUS-1 within the federal limits |
| NJ income-tax effect (6.37%) | $0 | $3,185.00 |
| NJ basis | $50,000 | $0 - deferrals are excluded and the employer share is deductible per NJ-BUS-1 (within the federal limits), so no NJ basis is created |
The $3,185.00 NJ figure is $50,000 × 6.37%: NJ guidance resolves the Solo 401(k) employer share affirmatively (NJ-BUS-1 permits deducting qualified self-employed 401(k) contributions up to the federal limits, and employer contributions to qualified plans receive tax-deferred treatment under NJ wage guidance), so both components reduce NJ income. Amounts above the federal limits are not deductible for NJ, and plan qualification and the taxpayer's facts still control. 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 §§401(k) and 402(e)(3) (elective-deferral exclusion) and §404(a) (employer-contribution deduction)
- 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 (federal IRA deduction excluded from the NJ computation)
- 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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