Most therapists we talk to know they should be putting money away for retirement and have a vague sense they are behind on it. That is such a common feeling in private practice that it is almost the default.
What usually stops people is not the saving. It is that opening a retirement account feels like one more admin task in a year already full of them, so it slides to January, then to “next year”, and eventually to a conversation with an accountant who has to explain that the window closed months ago.
The window is the thing worth understanding, because it is not one deadline. It is two; they fall in different places, and the one people miss is the earlier one.
What a Solo 401(k) Is For A Solo Therapist
A Solo 401(k) is a retirement plan built for people who work for themselves and have no full-time employees other than a spouse. If you run a solo practice, that is you, and you do not need a company or a payroll department to have one.
The reason it comes up so often for therapists is that you get to contribute twice. Once as the employee, out of what you pay yourself, and again as the employer, out of the practice. Most other retirement options only let you do one of those, which is why a Solo 401(k) usually lets a therapist put away considerably more than a traditional IRA or even a SEP-IRA would in higher-income years.
That is the appeal. The catch is entirely about timing, and it comes down to one date most people get wrong. Understanding the contribution limits helps, but the deadline is what actually trips people up.
How Much Can A Solo Therapist Actually Put Into a Solo 401(k) in 2026?
For 2026, the combined contribution limit is $72,000, according to IRS Notice 2025-67. That number has two parts: the employee deferral, which is the portion that comes out of your own pay, and the employer contribution, which comes from the practice side.
Very few solo practices get anywhere near that ceiling, and you do not need to in order for this to be worth doing. For most solo therapy practices, a realistic contribution is a meaningful fraction of annual net income, depending on your structure and how much you pay yourself. That fraction has a real effect on your taxable income for the year, and the right number is specific to your books.
The math is specific to your situation, which is why we always look at the actual numbers before giving a recommendation. What we can say is that for most solo therapists in private practice, the limit is not the ceiling they bump into. The December setup deadline is, and that is the part worth focusing on first.
The Solo 401(k) Deadline People Miss: December 31
To contribute for a given tax year, the plan has to be open by the last day of that year. Not funded. Open.
So if you want the contribution to count for 2026, the account has to exist and the paperwork has to be signed before the end of December. A plan you open in January cannot reach back and shelter last year’s income, no matter how much you meant to.
This is the deadline that catches people, because it feels like an administrative step rather than a financial one. Nothing has to leave your bank account by December 31. But something has to be set up.
Opening it is not hard. The big providers offer Solo 401(k) plans with no setup fee and it is mostly a form. What it does need is a few days of lead time, because providers get busy in December and you do not want to be doing this on the 30th. Once it exists, the money side comes down to a much later deadline.
Once the plan exists, the money has its own timetable, and this is where the rules become more forgiving rather than stricter.
When do Solo 401(k) Contributions Have To Be Paid?
Later than you would expect, and that is the good news.
Your own contribution, the part that comes out of what you pay yourself, generally needs to be sorted by the end of the year, and if you run payroll through an S-Corp, it flows through payroll like any other deduction.
The employer side is more forgiving. That contribution can be made right up until you file your return, extensions included. So you can open the plan in December, see what the year actually looked like once your books are closed, and decide how much to put in months later when you know the real number.
That sequencing is the practical point of this whole piece. Open early, decide late.
A therapist we worked with opened her Solo 401(k) in the second week of December, mostly because we reminded her, and put nothing in at the time. Her practice had a strong final quarter she had not anticipated. By the time we closed her books in February, she had a much clearer picture than she would have had in December, and she made a meaningful employer contribution against it before filing. If she had waited until the new year to open the account, none of that would have been available to her.
Nothing clever happened there. She just did the free, five-minute part on time and left the bigger decision until she had the information to make it.
What if You Miss the Solo 401(k) Deadline?
You have not missed everything, and it is worth knowing that before you write the year off.
A SEP-IRA (Simplified Employee Pension) can be opened and funded after year-end, right up to your filing deadline. It is simpler, it is genuinely useful, and for a therapist who has just realised in March that December went by without action, it is the option that still works.
The tradeoff is that a SEP-IRA only allows the employer-side contribution. There is no employee deferral on top, so for most therapists the ceiling is lower than a Solo 401(k) would have been. It also has no Roth option, so everything goes in pre-tax whether that suits your situation or not.
We cover how a retirement contribution changes what you owe in quarterly estimated taxes in our therapist estimated tax guide, since that is usually the next question people have once they set up the account.
One thing that shifts the mechanics of this, though, is how your practice is set up, so it is worth knowing which rules apply to your specific situation before you act.
Does Your Practice Structure Change The Solo 401(k) rules?
A bit, mostly in the mechanics rather than the deadline.
If you are a sole proprietor or a single-member PLLC, your contribution is calculated from your net self-employment income and it comes off your taxable income directly. You calculate the numbers when you file and the employer contribution goes in before that date.
If you have elected S-corp status, your own deferral runs through payroll, which means it has to be handled before the last pay run of the year rather than sorted out afterwards. That is a real difference in timing and worth flagging to whoever runs your payroll well before December.
If you are still weighing that decision, our S-corp vs PLLC calculator runs the comparison on your own numbers so you can see what the actual difference looks like for your practice.
Solo 401(k) Deadlines, In The Order They Arrive
Mid-November is when to make the decision, because it gives you room to open the plan without rushing.
December 31 is the hard one: the plan must exist. Nothing else about that date matters in terms of dollars.
Your filing deadline, extensions included, is when the employer contribution has to be in. That is the flexible part, and it is deliberately flexible so you can decide with real numbers rather than December guesses.
You do not need to know your final contribution figure in December. You need an open account in December. Those are very different jobs, and only one of them has a deadline you cannot move.
If you are not sure which option fits your practice or how much you could actually put away this year, let’s chat.
TL;DR:
A Solo 401(k) has to be open by December 31 to count for that year, but you have until you file to decide how much goes in. Miss the December date and a SEP-IRA is the fallback that still works after year-end.
