How much can you put in a solo 401(k) on $120,000 of profit?

On $120,000 of net self-employment profit, a sole proprietor under 50 can contribute about $45,804 to a solo 401(k) in 2025: the $23,500 employee deferral plus a 20% employer profit share, both capped by net earnings.

The breakdown

How much can you put in a solo 401(k) on $120,000 of profit?: $45,804
Net earnings (profit − half of SE tax): $111,522
Employee deferral (max $23,500): $23,500
Employer profit share (20%): $22,304
SEP-IRA ceiling for comparison: $22,304

How the assumptions move it

	Under 50	Age 50-59 (+$7,500)	Age 60-63 (+$11,250)
Solo 401(k) max	$45,804	$53,304	$57,054

Run your own numbers in the interactive calculator: Solo 401(k) / SEP-IRA calculator

The formula

Net earnings = profit − ½ SE tax. Max = min(deferral + catch-up, net earnings) + min(20% × net earnings, overall cap), never more than net earnings.

Assumptions on this page

2025 limits: $23,500 employee deferral, $70,000 overall cap, catch-ups of $7,500 (50+) and $11,250 (60-63). Sole proprietor math: employer share is 20% of net earnings after the half-SE-tax deduction.