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 annual additions cap for each employer[1][2] — with built-in handling for the SECURE 2.0 age 60–63 super catch-up and the Solo 401(k) employer contribution rules.

  • ✓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 (20% of net earnings after half of self-employment tax)
$0
$0$72,000
$

Net Profit (employer contribution up to 20% of net earnings after half of self-employment tax)

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. The Nonelective Contribution can be up to 25% of Compensation for an S Corporation owner. For a sole proprietor, the same 25% plan rate works out to 20% of net earnings from self-employment, figured after the deduction for half of self-employment tax and without deducting the contribution itself.[3][4][5]

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 the annual additions limit, which covers employer contributions such as the Solo 401(k)'s Nonelective Contribution, applies separately to each unrelated employer's plans[2]. 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 have a Solo 401k if I already have a 401k at my day job?

Yes. You can open a Solo 401k for your self-employed business while you participate in an employer's 401k. Your employee deferrals are shared across all 401k plans: combined, they can't exceed $24,500 in 2026 ($32,500 if you're 50-59 or 64+, or $35,750 if you're 60-63). If you defer $15,000 through your day job's 401k, you can defer only $9,500 more into your Solo 401k. Employer contributions aren't shared: your day-job match and your Solo 401k profit-sharing contribution each count only against their own plan's annual additions limit ($72,000 in 2026 before catch-ups).

How is the Solo 401k employer contribution calculated for sole proprietors vs S-Corps?

Sole proprietors and single-member LLCs can contribute up to 20% of their net self-employment income (business profit minus half of self-employment tax) as the employer portion, which works out to roughly 18.6% of profit. S-Corp and C-Corp owners can contribute up to 25% of their W-2 compensation. Either way, the compensation counted is capped at $360,000 for 2026.

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

The annual additions limit is $72,000 for 2026 (under 50). It caps the sum of employee deferrals, employer contributions and after-tax (mega backdoor) contributions in a plan. Plans of unrelated employers, such as a day-job 401k and your own Solo 401k, each get their own limit, but all the plans of one employer, or of businesses under common control, share one. Employee deferrals are capped across all plans either way.

What is the 2026 Solo 401k catch-up contribution for age 50+?

If you are age 50-59 or 64+, you can make an additional catch-up contribution of $8,000 in 2026, bringing your employee deferral limit to $32,500 and your total contribution limit to $80,000.

What is the age 60-63 super catch-up for a Solo 401k in 2026?

Under SECURE 2.0, participants aged 60-63 qualify for a higher "super catch-up" of $11,250 in 2026 (instead of the standard $8,000 catch-up). This raises their employee deferral limit to $35,750 and their total contribution limit to $83,250. At age 64 and older, the standard catch-up applies again.

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). Across unrelated employers they do not aggregate: each plan has its own annual additions limit. Plans of the same employer, or of businesses under common control, share one limit.

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.

Related Resources

Sources

  1. Notice 2025-67, 2026 Amounts Relating to Retirement Plans and IRAs, as Adjusted for Changes in Cost-of-Living — Internal Revenue Service. Verified November 3, 2026.
  2. Retirement topics - 401(k) and profit-sharing plan contribution limits — Internal Revenue Service. Verified November 3, 2026.
  3. Publication 560 (2025), Retirement Plans for Small Business — Internal Revenue Service. Verified November 3, 2026.
  4. One-Participant 401(k) Plans — Internal Revenue Service. Verified November 3, 2026.
  5. 26 U.S.C. §404. Deduction for contributions of an employer to an employees' trust or annuity plan and compensation under a deferred-payment plan — Office of the Law Revision Counsel, via GovInfo. Verified November 3, 2026.