You're a freelancer netting $120,000 in 2026. Here's the sequence.
Step 1 — Open the plan. Before December 31, 2026, open a Solo 401(k) at Fidelity (free, no account fees), Schwab (free), or E*Trade (free). The plan must exist by year-end for the 2026 tax year.
Step 2 — Decide on Roth vs traditional. Most providers default to traditional only; you must specifically request a plan with the Roth option. Ask for this up front.
Step 3 — Max the employee deferral. That's $24,500 (or $32,500 if 50+). This goes in through "salary deferrals" even though you're paying yourself via 1099 or draws. At Fidelity, this is a checkbox in the plan setup.
Step 4 — Fund the employer contribution. On $120,000 net, after the SE-tax adjustment, your employer portion is roughly 20% of net = $24,000. Total for the year: $24,500 + $24,000 = $48,500.
Step 5 — Deadline. You have until April 15, 2027, or October 15, 2027 with an extension, to fund both the employee and employer contributions for tax year 2026. But you must have opened the plan by Dec 31, 2026.
Step 6 — Form 5500-EZ. Once plan assets exceed $250,000, you file a short annual form. Miss it and penalties are meaningful. Set a calendar reminder.
See also: Solo 401(k) vs SEP-IRA comparison.