Can my spouse contribute to my Solo 401(k)?

Yes, if your spouse genuinely works in the business and is paid for it, they can participate in the same Solo 401(k) — this is one of the plan's hidden advantages. A spouse who earns compensation from the business can make their own employee deferral of up to $23,500 in 2025 (plus catch-up if 50+) and receive an employer profit-sharing contribution, effectively doubling the household's tax-advantaged saving. For a sole proprietor, this usually means putting the spouse on payroll or paying them a legitimate wage for real work. The plan stays a "Solo" 401(k) as long as the only participants are owners and their spouses; add a non-spouse employee and you'd need a full 401(k) with testing. Keep documentation that the spouse's pay reflects actual services rendered. Done right, a working couple can shelter a large chunk of household income.