An extension to file is not an extension to pay tax.
Delaware does not honor the federal extension automatically - a taxpayer must file Form PIT-EXT by the original due date to receive Delaware's own 6-month extension. Filing the form is what makes the extension automatic; there is no discretionary approval step once it is timely filed.
Not extended; interest and penalties accrue on any unpaid tax from the original due date
Authority
30 Del. C. §511 (extension of time for filing and payment)
Unlike most states on this site, Delaware requires an affirmative filing to get its extension - simply having a federal extension does not extend the Delaware due date.
The City of Wilmington's local Net Profits Tax is separate from this state return and has its own extension rule - see Wilmington, Delaware local tax extension.
Authority: 30 Del. C. §511 (extension of time for filing and payment). Sources: delcode.delaware.gov/title30/c005/sc02 (§511 text via law.justia.com); revenue.delaware.gov/personal-income-tax-forms; revenuefiles.delaware.gov/2021/TY21_PIT-EXT_2021-02_PaperInteractive.pdf.
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