Your Tax Year Is Bigger Than Your Calendar Year
Why Timing Matters More Than Most Taxpayers Realize
Self-employed taxpayers have many balls in the air, but you only need to catch one of them at a time.
A common misconception I see — even among highly educated professionals — is the belief that everything on your tax return has to happen between January 1st and December 31st.
It doesn’t.
In reality, the “tax year” is a series of rolling deadlines, stretching well into the following year. Understanding what must be done by when can make the difference between:
Missing valuable deductions
Creating unnecessary cash-flow stress
Or, conversely, strategically spreading deductions across multiple months while still getting credit for a single tax year
For physicians, business owners, and self-employed professionals, this timing flexibility is often the key to making aggressive tax planning actually work in real life.
Let’s walk through the major deadlines — and what actually needs to happen by each one.
By December 31st: The Hard Stop Items
Some deductions and elections truly do not survive the calendar year. If you miss these, they’re gone.
Retirement & payroll-related
Employee 401(k) contributions via payroll
“Elect” employee contributions to a Solo 401(k)
(there is an exception in place if the plan is newly established for that tax year).
Deductions that require cash leaving your account
State and local tax payments you want deducted in the current year
Charitable donations you want deducted that year
529 plan contributions that are deductible in most states
This is where timing and cash flow collide. If you’re planning to itemize or anticipate higher income in a future year, accelerating these payments into December can be incredibly powerful.
March 15th: Business Retirement Deadlines (No Extension)
If you operate through a partnership or S corporation and did not file an extension, this is your cutoff for:
Deductible retirement plan contributions for that entity
Miss this date without an extension, and the deduction is gone — even if you have the cash later.
April 15th: The Most Misunderstood Deadline
April 15th isn’t just “tax day.” It’s a major planning inflection point.
What must be completed by April 15th
Retirement plan contributions for a sole proprietor, if no extension was filed
IRA contributions for the prior year (even if you filed an extension)
HSA contributions for the prior year (even if you filed an extension)
Important nuance:
If you’re doing a Backdoor Roth IRA, the contribution goes on the prior-year return, but the conversion shows up on the return for the year the conversion actually happens — even if both steps occur close together.
State-specific twist
Some states — including Georgia, Kansas, Indiana, and Mississippi — allow deductible 529 plan contributions up until April 15th.
September 15th: Extended Business Plans
If an S corporation or partnership filed an extension, this becomes the new deadline for:
Completing deductible retirement plan contributions for that entity
This is often where high earners finally “catch up” once cash flow improves.
October 15th: Extended Sole Proprietors
For sole proprietors who filed an extension:
This is the final deadline to complete retirement plan contributions for the year
Miss this date, and the opportunity closes permanently.
Why This Matters: Cash Flow Isn’t Optional
Aggressive tax planning often looks great on paper — until someone realizes they’re supposed to come up with tens of thousands of dollars all at once.
Understanding these staggered deadlines allows you to:
Lock in deductions early
Fund them gradually
Align planning with real-world income patterns
Which brings us to a real-world example.
Case Study: Dr. Jones Learns That Timing Is a Tax Strategy
Dr. Jones is a self-employed cardiologist living in Chicago. In November 2025, he starts working with a new tax professional.
He’s been doing the basics:
Making estimated tax payments
Filing on time
Taking the standard deduction for the past five years
But he wants to know what else he can do to lower his tax bill.
Step 1: A Change in the Deduction Landscape
His tax pro explains that, due to recent changes in tax law, Dr. Jones will be able to deduct 100% of his state and local taxes for 2025.
That changes everything.
For the first time in years, he’ll be itemizing deductions, which means:
Charitable contributions are now deductible again
The timing of state and local payments suddenly matters
Step 2: December Planning (Without a Cash Hoard)
Dr. Jones isn’t sitting on a pile of savings — but he can save over $10,000 per month from ongoing earnings.
So in December 2025, he:
Contributes the maximum deductible amount to 529 plans for each of his two children.
Pays his city property taxes early, even though they aren’t due until January.
His tax pro warns him that if income rises in 2026, the enhanced SALT deduction could phase out.
Makes an estimated payment to Illinois after learning he’d otherwise owe money when he files.
Drops off a large donation to the Salvation Army after learning that a new tax bill will limit charitable deductions starting in 2026.
None of these actions required him to be wealthy — just informed and timely.
Step 3: Early 2026 — Using the Grace Period
With income earned in early 2026, Dr. Jones:
Funds $7,000 IRA contributions for both himself and his spouse.
Contributes $8,550 to a family Health Savings Account (HSA).
All of these count toward Tax Year 2025, even though the cash left his account in 2026.
Step 4: The Solo 401(k) Strategy
Dr. Jones establishes a Solo 401(k) early in 2026 with the plan to max out contributions for 2025.
His tax pro files an extension of his personal return, knowing April 15th won’t give him enough time to save.
Based on his net self-employment income, his tax pro confirms he can contribute the maximum:
$23,500 employee contribution
$47,500 employer contribution
$70,000 total
Between February and August, Dr. Jones contributes $10,000 per month, fully funding the plan well before the extended deadline.
Step 5: Momentum Into the Next Year
Starting in September, with the assistance of his tax pro, Dr. Jones begins the same process for Tax Year 2026.
He’s starting earlier, planning more deliberately, and not completing them at the last minute. In fact, he won’t even need to use an extension to postpone the 401(k) deadline.
The TaxSmart Takeaway
Your tax return is not confined to the calendar year — but your planning needs to respect the deadlines.
Understanding what must be done by:
December 31
March 15
April 15
September 15
October 15
can be the difference between:
Missed deductions
Forced cash crunches
And a tax strategy that actually fits your life
If you’re waiting until April to think about taxes, you’re already late.
Special Trivia Question!
Although the deadlines referenced above are pretty firm, what makes the tax code so complicated is that there are almost always exceptions to the rule.
What is one situation that permits IRA/HSA contributions to be completed after the hard deadline of April 15th?
A. First year contributions for a new account
B. Contributions for low-income taxpayers
C. Disaster relief
D. Contributions for taxpayers over age 65
Click here for the answer!