A catch-up contribution is an extra elective deferral that a 401(k) allows once you turn 50 during the year. For 2026 it is $8,000, or $11,250 if you are 60, 61, 62 or 63 at the end of the year. Catch-ups sit on top of the $72,000 415(c) limit, so a 55-year-old can put up to $80,000 into a Solo 401(k).
A cash balance plan has no catch-up, and does not need one: its limit already rises with age, because it is set by the benefit it may pay rather than by a yearly cap on what goes in. An owner with both plans keeps the full catch-up in the 401(k), since deferrals are left out of the combined deduction limit.
From 2026, catch-ups must be Roth contributions for anyone whose Social Security wages from the business sponsoring the plan were over $150,000 the year before. Roth money gives no deduction now. The test looks at W-2 wages, so it reaches S and C corporation owners but not sole proprietors or partners, whose self-employment income is not wages. See Roth catch-up contributions.