Solo 401(k) & Mega Backdoor Calculator
Plan your 2026 self-employed contributions and find out how much you can squirrel away in a Roth.
Last updated: April 2026
What is a Solo 401(k)?
A Solo 401(k) (also known as a Self-Employed 401k) is a powerful retirement plan for business owners with no employees (except a spouse). It offers some of the highest contribution limits in the US tax code.
The plan is unique because you wear two hats: the Employee (who can defer up to $24,000) and the Employer (who can contribute up to 25% of compensation). Total contributions for 2026 can reach $71,000 (plus catch-up).
How to use this calculator
- 1Business Net Income — Determine your expected annual profit (Revenues minus Expenses).
- 2Check Age — If you are 50 or older, you get an extra $7,500 in catch-up space.
- 3Other 401(k)s — If you have a W-2 job, those contributions count toward your $24,000 employee limit.
- 4Optimize for Roth — Check the Mega Backdoor space to see how much you can put into tax-free Roth accounts.
Formula & example
Max Total = Employee Deferral + Employer (20-25% of Net) + After-Tax Voluntary
If you earn $150,000 net, you can put $24,000 as an employee and ~$30,000 as an employer match. The remaining ~$17,000 can be contributed as after-tax 'Mega Backdoor' if your plan supports it.
Benefits
Highest Savings Limits
Much higher than a SEP IRA or SIMPLE IRA at similar income levels.
Roth Option
Unlike a SEP IRA, your employee portion can be 100% Roth.
Participant Loans
Solo 401(k)s often allow you to borrow against your balance if needed.
Use cases
Freelancers/Consultants
The gold standard for high-earning independent workers.
Side Hustlers
If you have a W-2 job but also a side business, you can use a Solo 401(k) for the side income.
Frequently asked questions
When is the deadline to open a Solo 401(k)?+
For a 2026 contribution, the plan must generally be established by December 31, 2026.
Can my spouse participate?+
Yes, if they work for the business, they can have their own employee and employer contributions within the same plan, effectively doubling your household savings.