#solo-401-k
One-participant 401(k) plans for self-employed individuals, contribution limits, and Roth options
Starting January 1, 2026, SECURE 2.0's Section 603 requires workers 50 and older with over $150,000 in prior-year FICA wages from the same employer to make 401(k) catch-up contributions — $8,000 standard, $11,250 for ages 60–63 — as after-tax Roth. Plans without a Roth option must amend by December 31, 2026 or bar catch-ups entirely; W-2 S-corp owners are in scope while K-1 partners are not.
For 2026 the IRS caps total 401(k) contributions at $72,000 versus a $24,500 employee deferral limit; business owners can convert the after-tax gap between the two into a Roth account tax-free using the mega backdoor Roth strategy.
Compare the 2026 Solo 401(k) and SEP-IRA limits side by side — when each plan wins, how the SECURE 2.0 super catch-up adds $11,250 for ages 60–63, the mega-backdoor Roth strategy for after-tax conversions, the 20% versus 25% Schedule C calculation, and the Form 5500-EZ filing required once plan assets cross $250,000.
Section 414(b), (c), and (m) treat related businesses as one employer for retirement-plan testing. This guide explains controlled-group and affiliated-service-group rules, the spousal and minor-child attribution traps, and the steps multi-business owners should take before opening a 401(k).
Section 4975 of the Internal Revenue Code defines disqualified persons and the six categories of forbidden transactions with self-directed IRAs and Solo 401(k)s. Violations trigger a 15 percent annual excise tax — and, for IRAs, deemed distribution of the entire account back to January 1.
A 2026 comparison of solo 401(k) and SEP-IRA plans for the self-employed, with contribution math at $60K, $120K, and $300K of net income, SECURE 2.0 Roth catch-up and super catch-up rules, setup deadlines, and a decision framework for picking the plan that shelters the most income.
Defined benefit and cash balance plans let high-earning solo professionals over 45 deduct $150,000 to $290,000 a year — three to four times what a SEP-IRA or Solo 401(k) allows. This guide walks through the contribution math, candidate profile, costs, deadlines, and how to stack a DB plan on top of a Solo 401(k).
A Solo 401(k) crosses into mandatory Form 5500-EZ filing once combined plan assets exceed $250,000 on the last day of the plan year. Late filings cost $250 per day up to $150,000 annually, but Rev. Proc. 2015-32 caps catch-up filings at $1,500 per plan if no penalty notice has been issued.
U.S. cash balance pension plans let solo doctors, attorneys, and consultants deduct $100,000–$370,000 a year on top of a Solo 401(k). 2026 contribution limits, a worked example for a 54-year-old physician, and the actuarial commitments to weigh before signing.
The Backdoor Roth IRA lets high earners contribute up to $7,500 a year to tax-free retirement growth by pairing a nondeductible traditional IRA contribution with a Roth conversion. Covers the five-step process, the pro-rata rule that derails most attempts, Form 8606 filing, and the recordkeeping that prevents being taxed twice.
In 2026, the Mega Backdoor Roth can move up to $47,500 of after-tax 401(k) money into Roth above the $24,500 elective deferral limit. This guide covers how the strategy works, the three plan features it requires, how the 401(k) pro-rata rule differs from the IRA version, and the mistakes that quietly erode its value.
In 2026, a self-employed person earning $100,000 can contribute about $18,587 to a SEP IRA versus $43,087 to a Solo 401(k). This guide compares 2026 contribution limits, Roth options, December 31 deadlines, and Form 5500-EZ filing thresholds so freelancers and consultants can choose the right plan.
