Delaware taxpayers face 9 separate tax deadlines in 2026, and missing a quarterly one is not a slap on the wrist: the IRS charges an underpayment penalty under IRC Section 6654 at the federal short-term rate plus 3 percentage points, computed quarter by quarter. Delaware returns are due April 30, later than the federal April 15, payments go through tax.delaware.gov/rptp/portal/home, and the top state rate is 6.6%.
1. March 16, 2026: S corporation and partnership returns are due
Form 1120-S and Form 1065 returns for tax year 2025 are due today, and every shareholder or partner is waiting on a Schedule K-1 before they can finish their personal return. If the books are not closed, file Form 7004 for an automatic extension to September 15, 2026.
Do this today: confirm your 2025 bookkeeping is closed and K-1s are on track before the deadline week.
2. April 15, 2026: Federal individual returns and 2025 balances are due
Form 1040 for tax year 2025 is due today. This is also the payment deadline: filing an extension moves your paperwork to October 15, 2026, but any tax you owe is still due now, and interest starts the day after.
Do this today: if you cannot file yet, pay your best estimate of the balance with the extension so interest never starts running.
3. April 15, 2026: Q1 estimated taxes are due for 2026
The Q1 federal estimated payment covers income earned January 1 to March 31. If you earn income without withholding, business profit, freelance work, rentals, or investment gains, the IRS wants its share now, not next April. Delaware expects its state estimate on the same schedule. Paying inside the safe harbor, 100% of last year's tax (110% for higher incomes) or 90% of this year's, keeps the underpayment penalty off the table.
4. The tip that replaces every date on this list
Nobody misses a quarterly payment because they cannot read a calendar. They miss it because the amount is a mystery: guessing what you owe feels bad enough to postpone. Amadae calculates your federal and Delaware quarterly estimates from your actual income as the year happens, then reminds you before every date on this page with the number already filled in.
That turns 9 deadlines into 9 confirmations.
5. April 30, 2026: Delaware individual returns are due
Delaware gives you until April 30, 2026 for the state return, later than the federal deadline. The extra time only applies to the state filing: the federal clock already ran out, and state tax owed is generally still due with the original deadline.
A bigger payment in Q4 does not undo the penalty that started accruing back in Q1.
6. June 15, 2026: Q2 estimated taxes are due for 2026
The Q2 federal estimated payment covers income earned April 1 to May 31. Delaware expects its state estimate on the same schedule.
7. September 15, 2026: Q3 estimated taxes are due for 2026
The Q3 federal estimated payment covers income earned June 1 to August 31. Delaware expects its state estimate on the same schedule.
8. September 15, 2026: Extended S corporation and partnership returns are due
If you filed Form 7004 in the spring, this is the real deadline for the 2025 1120-S or 1065. There is no second extension, and late pass-through returns are penalized per owner, per month.
9. October 15, 2026: Extended individual returns are due
The final stop for 2025 Form 1040 filings on extension. Remember that the payment was due back in April 15, 2026: October is a filing deadline, not a paying deadline.
10. January 15, 2027: Q4 estimated taxes are due for 2026
The Q4 federal estimated payment covers income earned September 1 to December 31. Delaware expects its state estimate on the same schedule.
11. Where to pay Delaware and federal taxes online
Federal balances and estimated payments are made at irs.gov/payments using IRS Direct Pay (no fee from a bank account) or EFTPS.
Delaware payments go through the state's official portal at tax.delaware.gov/rptp/portal/home. State estimates follow the same quarterly dates listed above.
12. Delaware income tax rates at a glance
Delaware uses a progressive income tax with 7 brackets and rates ranging from 0% to 6.6%.
Rates are based on the tax year 2025 published schedule. Brackets and deductions adjust periodically, so treat this as a planning guide rather than a filing reference.
13. Tax deadlines in states bordering Delaware
If you moved during the year, work across a state line, or file in more than one state, each state keeps its own filing calendar:
Planning ahead? See the Delaware tax deadlines for 2027.
14. Stop memorizing dates
Set a reminder for the next date on this list before you close the tab, or have a tax team compute the Delaware and federal numbers from your actual income and tell you before each one is due.
Book your free review before your next quarterly payment comes due. Deadlines for every other state are in our state tax deadlines index.