Multi-401(k) Contribution Calculator

Run a Solo 401(k) alongside a W-2 day-job 401(k)? This tool models contributions across every plan you have, enforcing the shared $24,500 employee deferral limit for 2026 and the $72,000 per-plan annual additions cap — with built-in handling for the SECURE 2.0 age 60–63 super catch-up and the Solo 401(k) 25%-of-profit employer rule.

  • ✓Solo 401(k) + W-2 401(k) side by side
  • ✓Shared employee deferral cap enforced live
  • ✓2025 + 2026 limits with age-based catch-ups
$72,000 Limit

Combined Totals Across All Plans

Employee
$20,000/ $24,500
81.6% of limit
After-tax (Roth)
$0
Employer
$15,000
Total Contributions
$35,000
Across 1 plan

Your Retirement Plans

My Solo 401(k)

Quick:
$20,000
$0$24,500
$15,000
$0$18,587.045 (~20% of net SE income)
$0
$0$72,000
$

Net self-employment profit (employer contribution ~20% after half-of-SE-tax deduction)

Total:$35,000 / $72,000

Remaining:$37,000

IRS contribution limits shown are for 2026 and subject to annual adjustment. This tool is for informational purposes only and does not constitute financial advice.

How the calculator works

Each plan you add becomes its own "bucket" with sliders for employee (pre-tax / Roth), after-tax, and employer contributions. The pie chart shows where you sit against that plan's annual additions limit. Across all buckets, the tool enforces the shared per-person employee deferral limit — move a slider on one bucket past the combined cap and the others shrink to make room. Switch a bucket between W-2 401(k) and Solo 401(k) and the employer-side controls swap between an employer-match calculator and the Solo 401(k) profit-sharing cap — with a Sole Prop / S-Corp toggle that picks the right math (20% of net SE income vs 25% of W-2 wages).

Why this matters for Solo 401(k) owners

A surprising number of Solo 401(k) owners also have a W-2 day job with its own 401(k). The IRS treats employee deferrals as a per-person limit across all 401(k)s, but employer contributions — including the Solo 401(k)'s 25%-of-profit profit-sharing — are calculated per plan. Get the split wrong and you either leave money on the table or trigger an excess-deferral correction. The calculator makes the trade-off visible.

Multi-401(k) Contribution Calculator FAQ

Can I contribute to both a Solo 401(k) and a W-2 employer 401(k) in the same year?

Yes. The IRS lets one person participate in multiple 401(k) plans at the same time. The catch is the employee deferral limit ($24,500 in 2026, plus catch-ups if you're 50+) is a combined per-person cap across all plans, not per-plan. The annual additions limit ($72,000) — which includes employer contributions — is per plan and is not aggregated, which is what makes running a Solo 401(k) alongside a W-2 401(k) so powerful.

How does the shared employee deferral limit work?

Every dollar you defer pre-tax (or Roth) into any 401(k) plan counts against the same $24,500 ceiling for 2026. If you defer $15,000 through your day job's 401(k), you can only defer another $9,500 into your Solo 401(k) — the calculator enforces this automatically as you move sliders across plans.

How is the Solo 401(k) employer contribution capped?

It depends on your business structure. If you're an S-Corp or C-Corp owner contributing off W-2 wages, the employer (profit-sharing) cap is 25% of those wages. If you're a sole proprietor or single-member LLC, you have to subtract half of your self-employment tax from net business profit first, then apply 20% — which works out to roughly 18.6% of profit. Toggle Sole Prop / S-Corp inside each Solo 401(k) bucket and the calculator applies the correct cap (and the $350,000 maxCompensation cap for 2026) to the employer slider automatically.

What is the per-plan 415 / annual additions limit?

Each plan has its own annual additions cap — $72,000 for 2026 (under 50). This is the ceiling for the sum of employee deferrals + employer contributions + after-tax (mega backdoor) contributions in that single plan. Because it's per-plan, having two plans effectively doubles your potential after-tax / employer contribution headroom — but employee deferrals are still capped across both.

How do age-based catch-up contributions work in 2026?

If you're 50–59 or 64+, you can defer an additional $8,000 on top of the standard $24,500, bringing the employee deferral cap to $32,500. SECURE 2.0 introduced an enhanced catch-up for ages 60–63 specifically: $11,250 instead of $8,000, raising the per-plan annual additions limit to $83,250. At age 64+ you revert to the standard catch-up. Set your age in the calculator and the limits update automatically.

What counts as "employee" vs "employer" contributions when I have multiple plans?

Employee contributions are your elective deferrals — pre-tax or Roth — that come out of your paycheck or earned income. They share one combined per-person limit across all your plans. Employer contributions include matching contributions from a W-2 employer and the profit-sharing contribution from your own business in a Solo 401(k). They do not aggregate across plans, but each plan still has to fit within its own per-plan annual additions cap.

Should I consult a CPA before maxing multiple plans?

Yes — especially if you're juggling a W-2 401(k), a Solo 401(k), and any after-tax / mega-backdoor strategy. Excess deferrals trigger double taxation if not corrected by April 15 of the following year, and the per-plan vs cross-plan rules around employer contributions, controlled-group restrictions, and SECURE 2.0's Roth catch-up mandate (for high earners) all benefit from a qualified tax professional's review.

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