Miss Bonnie MD is now Wealthy Mom MD!

The Solo 401(k)

I’ve waxed on about why I love the Roth IRA. I also love the Solo 401(k). Also known as an individual 401(k) or solo-K, it is a tax-sheltered retirement account for really small businesses – just you. This two part article will discuss the solo-K in the context of having a main job (w2) and having a side job with 1099 income – such as moonlighting, a blog, completing medical surveys etc. Although it will also apply if you have 1099 income alone as well. With this really small business you are considered to be both the employEE and employER. Your spouse can also work for you and qualify to participate, but no other employees. Why is the solo-K so great?

  1. Ability to contribute up to $54K*
You’re limited to a maximum $18K employEE contribution through your work-sponsored 401(k)/403(b). The IRS allows your employer to make additional “profit-sharing” contributions of $36k for a total of $54k. Unfortunately, while many of us have employer “matches”, we don’t work for employers with profit-sharing plans. But if you open a solo-k for your small business, you can make both employEE and employER contributions up to the current max of $54K. Keep in mind that if you have multiple work 401(k)s, you’re limited to one $18K employee contribution across all accounts. But you can make “profit-sharing” contributions of 20% of net income to your solo-K even if you’ve contributed $18k as an employEE. Like regular 401(k)s you can elect pre-tax (or traditional) employee contributions or after-tax, or Roth contributions. Employer contributions are always pre-tax.
  1. Ability to hire your spouse
This is a great perk if you have a stay at home spouse who would only have access a spousal Roth IRA. Hire your spouse and s/he will be able to contribute $18K as an employee. Win-win.
  1. Ability to roll over other retirement accounts into it
This is huge. As life goes on you’ll change jobs at least a few times. This often leaves a trail of “orphan” 401(k’s)/403(b’s). You may have rolled over one or more of these into an IRA or two. It can get really messy. Not to mention that you’re probably paying a maintenance fee for all of the accounts. Set up a solo-K and you can roll all these orphans into it, consolidating everything into one account. Less paper, less emails, and easy to keep track of your investment plan. It’s retirement account decluttering at its best.
  1. Ability to contribute to a backdoor Roth IRA without being subject to the pro-rata rule
After you move all your old accounts (namely, anything with “IRA” in the name), you now have a clean slate to begin contributing to a backdoor Roth IRA. If you have any other non-zero balances in any IRA account, you’ll be subject to the pro-rata rule if you contribute to a backdoor Roth IRA, which means you’ll pay unnecessary extra taxes. Not good. You’re convinced you need one now, right? Can I open one? Maybe or maybe not. You need earned income, typically as an independent contractor (IC). If you own an S-corp with no employees, this would come from your W2 income. For physicians, however, this is typically IC income from moonlighting, income from surveys, speaker fees, etc. If you don’t have any of these now, you can find this kind of work pretty easily. I only made $1000 of IC income, can I and is it worth opening a solo-K? Yes and yes! You need only the minimum a custodian (aka brokerage firm) requires to open a solo-K. There are no “required minimum” contributions to make to a solo-K. It is worth opening for the ability to roll over other retirement accounts into it (see #4 above). What else do I need to know?
  • Once the balance in the solo-K reaches $250K you’ll be subject to some compliance measures including filing form 5500 with the IRS annually.
  • You need to open the solo-K by 12/31 of the calendar year but you’ll have until tax day, including extensions, to fund it. So the absolute latest you can fund it is by 10/15 the following year.
Read on for the second part of this topic where I’ll discuss why you should choose a solo-K over a SEP-IRA and where you should open your solo-K. *2017 limits. If you are age 50+, you can add another $6k to your employee contributions. Do you have a solo-K? Comment below!]]>


  1. Christine Chen on July 16, 2017 at 12:19 pm

    My current FA (working on independence) states that investment profile in my TIRA is different from what you can do with solo401k, is it true? His claim is that better investment in TIRA accounts. I have about 200k+ in my ira and try to roll to solo 401 k to be able to do backdoor Roth and that’s what he said.

    Second question is why sol401 is better than SEP? I have SEP from 1099 currently and contribute 20% ( I maxed w w2 and profit sharing).

    Third question is that I also have another LLC which will generate K1 income, can I set up another retirement account or it’s too much invitation for IRS audit? If not for me then for the spouse? He has w2 only.

    Thanks so much.

    • Miss Bonnie MD on July 16, 2017 at 2:17 pm

      1) I don’t think so.You can own i-stocks and index funds in a solo-K, you prolly won’t be investing in much else in those accounts for now
      2) This will be addressed in part 2 – but you can’t do a backdoor Roth IRA if you have a SEP and you cna generally contribute more to a solo K than a SEP.
      3) Sorry, I don’t really know anything K1 income….

      I don’t like what your FA is telling you tho btw …

  2. Future Proof MD on July 16, 2017 at 12:52 pm

    Thanks for sharing Miss Bonnie! I’ve been a big fan of SE401k myself and just recently opened one at Fidelity. I initially intended for it to be a pitstop for my future Backdoor Roth conversions (currently I make so little money I can still use the front door). But I think I might just leave it open for self employment income generated thru Future Proof MD instead.

    • Miss Bonnie MD on July 16, 2017 at 2:15 pm

      welcome! Yep, you’ll need it soon I hope 🙂

  3. cargcar on July 17, 2017 at 7:10 am

    Wonderful post. Thank you! One of the clearest posts that I have seen regarding opening a solo 401k. You have inspired me to take the plunge.

    • Miss Bonnie MD on July 17, 2017 at 8:49 am

      Thank you! And best of luck.

  4. MKK on July 17, 2017 at 8:55 am

    My husband has a very small at-home business, so I had him open a solo 401K with Fidelity, mostly so he could move IRA $$ into it and avoid the backdoor. He ended up opening a Keogh account, though. Is this the same as a 401k? For tax and back-door purposes, it sure seems to be. Thanks!

  5. MIS on January 17, 2018 at 1:56 pm

    I opened both a Roth solo 401k and a pretax solo-401k. I am an independent contractor with 1099 income and am currently just a sole proprietor. I plan to put the $18,500 employEE contribution into the Roth solo 401k. Can I put the 20% employER profit sharing portion in as a sole proprietor or do I have to set myself up as an LLC to do this?

    • Miss Bonnie MD on January 20, 2018 at 6:58 am

      Yes to the ~ 20% net profit as employer portion! Don’t need an LLC.

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