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If you are an adult in the US with ADHD who filed a Form 4868 extension and then let October 15, 2026 slip by, filing your 2025 return on December 15 instead of December 14 raises the IRS late-filing penalty on a $1,200.00 balance from $108.00 to $525.00. That one day costs $417.00.
| You file and pay | Late-filing penalty | Total on top of the tax |
|---|---|---|
| By November 15, 2026 | $54.00 | $145.25 |
| By December 14, 2026 | $108.00 | $211.92 |
| On December 15, 2026 | $525.00 | $629.15 |
| By January 15, 2027 | $525.00 | $642.29 |
The figures come from the planner's own formulas, recalculated in LibreOffice and checked against the browser version: $1,200.00 of 2025 tax unpaid on April 15, 2026, a valid extension, and payment on the day you file.
Why the jump happens on December 15
With an extension, the late-filing penalty starts the day after October 15. It is 5% of the unpaid tax for each month or part of a month, but the IRS subtracts the 0.5% late-payment penalty for the same month, so you pay 4.5% a month for up to five months. Two months on $1,200.00 is $108.00.
There is a second rule. When a return is more than 60 days late, the late-filing penalty cannot be less than $525 or 100% of the unpaid tax, whichever is smaller. That is the amount for returns due in 2026, listed in the IRS manual at IRM 20.1.2.3.7.4. The manual also says the late-payment offset does not take the penalty below that minimum. Day 60 after October 15 is December 14, 2026, so filing on December 15 puts the return on day 61.
For balances under about $2,333, the $525 minimum is larger than five full months at 4.5% (22.5%) would ever be. Smaller balances therefore feel the floor hardest. If you owe $400, the minimum is the full $400.
What keeps running whether or not you filed
The late-payment penalty has run since April 15, 2026 at 0.5% a month: an extension gives you more time to file, not more time to pay. By December 15 that is eight months, or $48.00 on $1,200.00. Interest runs too: the IRS rate for October to December 2026 is 7% a year, compounded daily. The planner shows a simple-interest estimate on the tax only ($56.15 to December 15), so your notice can differ by a few dollars.
No extension at all?
Without Form 4868, the return was due April 15, 2026 and is already past the five-month cap. On $1,200.00 the 4.5% rate gives $270.00, but the $525 minimum applies, so filing on October 18 still means $525.00 plus $42.00 late-payment penalty and about $42.81 interest. There is no cheaper date left. The planner shows that case when you set the extension field to 0.
How to use the free planner
Enter what you still owe for 2025 and how many days after October 15 you expect to file and pay. Leave the minimum at $525 and the interest at 7% unless the IRS changes them. You see the months late, both penalties, the floor, the interest estimate, the total, and what filing by December 14 would save. Nothing is uploaded.
The full version is an .xlsx with the same formulas plus a file-by ladder for November 15, December 14 and January 15. You keep it, rerun it if your balance changes, and show it to whoever helps with your taxes.
What to do this week
Put December 14, 2026 in your calendar as the file-by date, not the due date. File even if you cannot pay everything, because the late-filing penalty is the bigger one. If your last three years were clean, ask the IRS about First-Time Abatement. For returns due in 2027, the minimum rises to $535.
15 seconds — what it actually does
Questions people ask
What does this ADHD planner calculate?
You enter the 2025 tax you did not pay by April 15, 2026, whether you filed Form 4868, and how many days after October 15, 2026 you will file and pay. It applies the IRS late-filing rate of 4.5% a month after the 0.5% late-payment offset, the $525 minimum for returns more than 60 days late, and 7% interest, then shows the total and the cost of missing December 14.
Who is this planner for?
US adults with ADHD, or anyone fighting time blindness, who filed an extension for their 2025 Form 1040, owe a balance, and let October 15, 2026 slip by. It turns a vague 'I should do my taxes' into one dated target, December 14, 2026, and shows in dollars what each later date costs on your own balance.
Why not just use a free printable ADHD planner?
A printable planner gives you a box to write 'taxes' in. It does not know that the IRS minimum late-filing penalty for returns due in 2026 is $525 or 100% of the unpaid tax, or that it starts once the return is more than 60 days past the extended deadline. On $1,200 owed, one day turns $108 into $525.
What do I get free, and what is in the paid file?
Free, in the browser: the full answer for your own return, with each penalty, the interest estimate, the total and the Dec 14 saving. Paid, one payment and not a subscription: the .xlsx with the same live formulas plus a file-by-date ladder for Nov 15, Dec 14 and Jan 15 that you keep, rerun and show your tax preparer.
How does the $21 compare with the penalty?
On the example balance of $1,200, filing on December 15, 2026 instead of December 14 adds $417 in late-filing penalty, because the $525 minimum replaces the $108 that 4.5% a month would give. The planner shows that gap for your own balance before the date passes. It estimates; your IRS notice is the final number.
When do these numbers change next?
For returns due after December 31, 2026, so your 2026 return due April 15, 2027, the IRS minimum late-filing penalty rises from $525 to $535 (IRM 20.1.2.3.7.4, revised 12-30-2025). The underpayment interest rate is reset every quarter; 7% applies to October through December 2026. Update both inputs when the IRS announces new figures.
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