What to Include When Mailing a Federal Tax Return?

When mailing a federal tax return, your envelope needs a signed Form 1040 with every applicable schedule stacked in sequence-number order behind it, any W-2 or 1099 forms showing federal income tax withheld stapled to the front, and — if you owe a balance — a check made out to “United States Treasury” tucked in loose with Form 1040-V. For the 2025 tax year, the filing deadline is April 15, 2026.¹ Getting the contents right, and picking the correct mailing address, is what keeps a paper return from stalling in processing.

The Forms That Go in the Envelope

The core document is Form 1040, or Form 1040-SR if you are 65 or older. Federal law requires you to report your income on the forms the IRS prescribes.² Fill in your name, address, and Social Security number exactly as they appear on your Social Security card.

Behind the 1040, include every schedule and additional form that applies. Schedule A for itemized deductions, Schedule C for business income, Schedule SE for self-employment tax, and so on. Each schedule shows a sequence number in the upper-right corner. Stack them in that numerical order so the processing agent can work through the return in the order the IRS expects.

W-2s and 1099s That Show Withholding

Your employer issues a W-2 reporting your wages and the federal income tax withheld during the year.³ Other income documents, such as a 1099-R for retirement distributions or a 1099-INT for interest, may also show withheld tax. Employers and payers generally must furnish these forms by January 31.

Only include forms that actually show federal income tax withholding. Check the “Federal income tax withheld” box on each W-2 or 1099. If the amount is blank or zero, leave that form out. Attaching documents without withholding data just adds bulk and slows the manual keying of your return.

Identity Protection PIN

If the IRS has issued you an Identity Protection PIN, write it in the IP PIN field near the signature area on Form 1040. A missing or wrong IP PIN will hold up your paper return while the IRS verifies your identity.⁴ If your spouse or a dependent also has one, include theirs too.

Separately, if you are a victim of tax-related identity theft and cannot e-file because someone else already used your Social Security number, attach Form 14039 (Identity Theft Affidavit) to the back of your paper return and mail everything to your normal filing address.⁵

How to Assemble and Sign the Pages

Staple your W-2s (and any 1099s that show withholding) to the front of Form 1040 with a single staple in the upper-left margin, clear of any numbers. Those withholding documents sit on top so the agent can quickly confirm what you have already paid. Behind Form 1040, place your schedules and additional forms in sequence-number order.

Your return is not valid until you sign it. If you are filing jointly, both spouses must sign.⁶ By signing, you declare under penalty of perjury that the information is true and correct. Date each signature line as well.

An unsigned return will not be accepted for processing. The IRS will mail it back and ask you to sign and resubmit, which delays any refund and pushes back the date your return counts as filed. Do a page-by-page check before you seal the envelope.

If You Owe a Balance

When your return shows tax due, include the payment in the same envelope. Form 1040-V (Payment Voucher) helps the IRS credit your payment to the right account and year.⁷ The voucher asks for your name, Social Security number, the amount you are paying, and the tax year.

Make the check or money order payable to “United States Treasury.” On the payment itself, write your Social Security number, daytime phone number, and “2025 Form 1040” so it cannot be misapplied. Do not send cash.⁷

Place the check and Form 1040-V loose in the envelope. Do not staple or paperclip them to the return or to each other.⁷ Keeping the payment loose lets the IRS route it for deposit separately from the return itself.

Paying Electronically Instead

You can still file on paper and pay online. IRS Direct Pay draws from your bank account for free.⁸ Debit card, credit card, and the Electronic Federal Tax Payment System (EFTPS) are also options. If you pay electronically, do not include a check or Form 1040-V in your envelope. Just send the return.

Where to Mail It

The correct IRS address depends on your state and on whether you are enclosing a payment. Returns with a check go to a different processing center than returns without one.⁹ Look up the exact address for your state in the Form 1040 instructions or on the IRS “Where to File” page. Using the wrong one can significantly delay processing and any refund.

Proving You Filed on Time

Under federal law, the postmark on your mailing is the date you filed.¹⁰ A return postmarked April 15 counts as on time even if it arrives days later. Dropping the envelope into a regular mailbox without a receipt gives you nothing to fall back on if the IRS later says your return arrived late or never arrived.

The statute names U.S. registered mail as prima facie evidence of delivery, with the registration date treated as the postmark date.¹⁰ Certified mail with a return receipt is also accepted under IRS regulations, and most filers use it.

Approved Private Carriers

The IRS also accepts specific private carrier services under the timely-mailing rule. Not every FedEx or UPS option qualifies. The approved services are:¹¹

DHL Express 9:00, 10:30, 12:00, Worldwide, Envelope, and Import Express
FedEx First Overnight, Priority Overnight, Standard Overnight, 2 Day, and several international services
UPS Next Day Air Early A.M., Next Day Air, Next Day Air Saver, 2nd Day Air, 2nd Day Air A.M., and Worldwide Express options

Ask the carrier how to obtain written proof of your shipping date, since it works differently from USPS certified mail.

If You Need More Time

File Form 4868 by April 15, 2026, for an automatic six-month extension that moves the filing deadline to October 15, 2026. An extension gives you more time to file, not more time to pay. Interest and penalties on unpaid tax start accruing after April 15 regardless.¹² Estimate what you owe and send a payment with Form 4868, or pay online, to hold those charges down.

What to Keep After You Mail

Photocopy everything before it goes in the envelope: the signed return, all attachments, the check or voucher, and your certified mail or carrier receipt. Those copies are your record if a document is lost in transit or the IRS raises a question later. Paper returns typically take six or more weeks to process, and any correspondence from the IRS about your return will come by mail — the agency does not call to request personal information.¹³

1
Internal Revenue Service. IRS Announces First Day of 2026 Filing Season
2
Office of the Law Revision Counsel. 26 USC 6011 – General Requirement of Return, Statement, or List
3
Internal Revenue Service. General Instructions for Forms W-2 and W-3 (2026)
4
Internal Revenue Service. Get an Identity Protection PIN
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IRS.gov. Form 14039 Identity Theft Affidavit
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Internal Revenue Service. Signing the Return
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IRS.gov. Form 1040-V (2025) Payment Voucher for Individuals
8
Internal Revenue Service. Direct Pay Help
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Internal Revenue Service. Where to File Paper Tax Returns With or Without a Payment
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Office of the Law Revision Counsel. 26 USC 7502 – Timely Mailing Treated as Timely Filing and Paying
11
Internal Revenue Service. Private Delivery Services (PDS)
12
IRS.gov. Form 4868 – Application for Automatic Extension of Time to File U.S. Individual Income Tax Return
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Internal Revenue Service. Refunds