When you file a federal tax return on paper, you need to send Form 1040 along with Copy B of every W-2, any 1099-R or W-2G that shows federal tax was withheld, Form 2439 if you received one, every numbered schedule that feeds a line on your 1040, any form required for a credit you’re claiming, and Form 1040-V with a check if you owe. If you e-file, your software transmits all of that digitally and you send nothing by mail. What to send with your tax return depends on your income sources, the credits you claim, and whether you owe money or expect a refund.
Income Documents You Attach
Paper filers attach these to the front of Form 1040:
- Copy B of every Form W-2 you received.
- Form W-2G, if a casino, lottery office, or other payer withheld federal tax from gambling winnings.
- Form 1099-R, only if it shows federal income tax was withheld from a pension, annuity, IRA distribution, or similar payout.
- Form 2439, if a mutual fund or REIT sent you one for undistributed capital gains.
The IRS 1040 instructions are specific: attach W-2s and Form 2439 to the front of your return, and include W-2G and 1099-R forms only when they show tax withheld.1Internal Revenue Service. Instructions for Form 1040 The physical copies let the IRS match your reported numbers against what employers and payers already submitted. If figures don’t line up and the form isn’t in the envelope, you’ll get a notice, which delays your refund or produces a proposed adjustment.
1099s You Do Not Attach
A common mistake is stuffing every 1099 you received into the envelope. Most are for your records. Form 1099-NEC, which freelancers and independent contractors receive, says “keep for your records” right on Copy B.2IRS: Form 1099-NEC (Rev. April 2025). Form 1099-NEC You report that income on Schedule C or on Schedule 1’s “Other income” line, but the 1099-NEC itself stays home. The same goes for 1099-INT, 1099-DIV, and 1099-MISC when no federal tax was withheld. The 1040 instructions put it plainly: don’t attach correspondence or other items unless specifically required.1Internal Revenue Service. Instructions for Form 1040 No receipts, no bank statements, no explanation letters. Keep those in your own files.
Schedules Behind Form 1040
Any numbered schedule that has a corresponding entry on Form 1040 must go with the return. The main ones:
- Schedule 1 for additional income (freelance earnings, unemployment, alimony received, prizes) and above-the-line adjustments like student loan interest, educator expenses, and HSA contributions.1Internal Revenue Service. Instructions for Form 1040
- Schedule 2 if you owe the alternative minimum tax, need to repay excess advance premium tax credits, or owe self-employment or household employment tax.
- Schedule 3 for nonrefundable credits like the foreign tax credit and education credits, plus other payments such as estimated tax you already sent in.
- Schedule A if you itemize instead of taking the standard deduction, covering medical expenses over 7.5% of AGI, state and local taxes, mortgage interest, and charitable contributions.3Internal Revenue Service. 2025 Instructions for Schedule A (Form 1040) – Itemized Deductions
- Schedule C for sole proprietors and independent professionals reporting business receipts, expenses, and net profit.4Internal Revenue Service. Instructions for Schedule C (Form 1040) (2025)
Other schedules apply in specific cases: Schedule B for interest and dividends over $1,500, Schedule D for capital gains and losses, Schedule E for rental income and partnership income, and Schedule SE for self-employment tax. Each schedule has an Attachment Sequence Number printed in its upper-right corner that tells you the order to stack them behind Form 1040.
Forms Required for Specific Credits
Several credits require their own form. Leaving one out doesn’t only cost you the credit; in some cases it blocks you from claiming it in future years.
Child Tax Credit
Schedule 8812 calculates the child tax credit, the credit for other dependents, and the additional child tax credit. If you claim any of these, the completed schedule goes with your return.5IRS.gov. 2025 Instructions for Schedule 8812 (Form 1040) If the IRS previously denied or reduced your child tax credit for any reason other than a math error, attach Form 8862 to reclaim it.
Education Credits
Form 8863 is required for the American Opportunity Credit or the Lifetime Learning Credit. For the American Opportunity Credit, you must enter the school’s employer identification number on the form. If that credit was denied in a prior year, attach Form 8862 as well.6Internal Revenue Service. Instructions for Form 8863 (2025)
Premium Tax Credit
If you bought health insurance through the Marketplace and received advance payments of the premium tax credit, you must file Form 8962 and attach it to your return to reconcile those payments, even if you wouldn’t otherwise be required to file.7Internal Revenue Service. 2025 Instructions for Form 8962 Skip that step and two things happen: your refund is delayed, and the IRS may cut off your advance credit payments for future years, leaving you responsible for the full monthly premium out of pocket.8Internal Revenue Service. Premium Tax Credit: Claiming the Credit and Reconciling Advance Credit Payments
You do not attach Form 1095-A. Keep it for your records and use the information on it to complete Form 8962.9Internal Revenue Service. Questions and Answers About Health Care Information Forms for Individuals The same goes for Forms 1095-B and 1095-C from employer-sponsored coverage.
Foreign Financial Assets
If you hold financial accounts or assets outside the United States above certain thresholds, you must attach Form 8938 (Statement of Specified Foreign Financial Assets). The filing thresholds depend on filing status and where you live:
- Single filer in the U.S.: total foreign asset value over $50,000 on the last day of the year or $75,000 at any point during it.
- Married filing jointly in the U.S.: over $100,000 on the last day or $150,000 at any point.
- Filing abroad, not jointly: over $200,000 on the last day or $300,000 at any point.
- Filing abroad, jointly: over $400,000 on the last day or $600,000 at any point.
The penalty for not filing Form 8938 when required is $10,000. If you still don’t file after the IRS sends a notice, an additional $10,000 penalty accrues for every 30-day period the failure continues, up to $50,000.11eCFR. 26 CFR 1.6038D-8 – Penalties for Failure to Disclose Claiming that a foreign country would punish you for disclosing the information is explicitly not a valid excuse.
If You Owe a Balance
How you pay determines what else goes in the envelope.
Paying by Check or Money Order
Include Form 1040-V (Payment Voucher) with your check or money order. The voucher links the payment to your tax account.12Internal Revenue Service. Form 1040-V, Payment Voucher (2025) A few rules:
- Make the check payable to “U.S. Treasury.”
- Write your Social Security number, the tax year, and “Form 1040” on the check.
- Do not staple or clip the check or voucher to the return. Put them loose in the envelope.
Your mailing address changes when a payment is enclosed. The IRS routes returns with payments to different processing centers than returns without, so verify the correct address for your state before sealing the envelope.14Internal Revenue Service. Where to File Addresses for Taxpayers and Tax Professionals Filing Form 1040
Paying Electronically
Pay electronically and you don’t need Form 1040-V at all. IRS Direct Pay sends a payment from your bank account for free with no registration; you get a confirmation number immediately, and the payment posts within one to two business days.15Internal Revenue Service. Pay Personal Taxes From Your Bank Account The Electronic Federal Tax Payment System (EFTPS) is another option. Either way, no voucher, no check, and one fewer source of processing errors.
Signing the Return
An unsigned return isn’t a valid return. For paper filing, sign and date the bottom of Form 1040. Joint filers both sign; a missing spouse signature is one of the most common reasons paper returns come back. For e-filed returns, you sign with a self-select PIN, any five-digit number other than all zeros, and it serves as your digital signature.16Internal Revenue Service. Self-Select PIN Method for Forms 1040 and 4868 Modernized e-File (MeF)
Identity Protection PIN
If the IRS assigned you an Identity Protection PIN, enter it on your return. This six-digit number confirms your identity and prevents someone else from filing under your Social Security number. If you’re claimed as a dependent and have an IP PIN, the person claiming you must enter it on their return. An e-filed return missing a required IP PIN is rejected outright.17Internal Revenue Service. Frequently Asked Questions About the Identity Protection Personal Identification Number (IP PIN)
Assembling and Mailing a Paper Return
Stacking order matters. IRS processing expects this sequence:
- Front of Form 1040: W-2s, W-2G, Form 2439, and any 1099-R showing withholding.
- Behind Form 1040: schedules and additional forms in order of their Attachment Sequence Number (upper-right corner).
- Any required supporting statements last, in the same order as the schedules they support.
If you owe, place the check and Form 1040-V loose in the envelope. Mail to the IRS address assigned to your state, which depends on where you live and whether you’re enclosing a payment.14Internal Revenue Service. Where to File Addresses for Taxpayers and Tax Professionals Filing Form 1040 Sending to the wrong address doesn’t invalidate the filing, but it can add weeks of delay.
Proof of Timely Filing
A regular stamp gets your return there but gives no proof of the mail date. Under federal law, the postmark date counts as the filing date, and certain mailing methods create legal proof.19Office of the Law Revision Counsel. 26 U.S. Code 7502 – Timely Mailing Treated as Timely Filing and Paying USPS registered mail is prima facie evidence of delivery. Certified mail with a return receipt gives you a tracking number and delivery confirmation. The IRS also recognizes specific service levels from DHL Express, FedEx, and UPS as designated private delivery services.20Internal Revenue Service. Private Delivery Services (PDS) Not every FedEx or UPS option qualifies; standard FedEx Ground and UPS Ground do not.
What Changes When You E-File
E-filing eliminates most of the paper assembly. Your software bundles every schedule and form into one digital transmission. No W-2s to staple, no sequence numbers, no mailing address to verify. The software flags missing schedules before you submit, which heads off the incomplete-return problem that plagues paper filers. After transmission, you receive an electronic acknowledgment from the IRS with a timestamp; that acknowledgment is your proof of filing, so certified mail is unnecessary.16Internal Revenue Service. Self-Select PIN Method for Forms 1040 and 4868 Modernized e-File (MeF) If you owe, you can pay electronically at the same moment you file, and the software links the payment to the return.
What Happens If Something Is Missing
A return arriving without a required schedule or form usually gets flagged in processing. In simple cases, the IRS sends a notice asking for the missing document, and your refund waits weeks or months. In more serious cases, the IRS may calculate your tax based on income reported by employers and financial institutions, then send a proposed adjustment or notice of deficiency.21Internal Revenue Service. Understanding Your CP3219N Notice Those IRS-calculated returns rarely help you, because they omit deductions and credits you didn’t document.
The failure-to-file penalty under federal law starts at 5% of the unpaid tax for each month the return is late, capping at 25%. If you file more than 60 days after the deadline, the minimum penalty is the lesser of $525 (for returns due in 2026) or 100% of the tax owed.22Internal Revenue Service. Topic No. 653, IRS Notices and Bills, Penalties and Interest Charges23Office of the Law Revision Counsel. 26 USC 6651 – Failure to File Tax Return or to Pay Tax An incomplete return that the IRS can’t process may be treated as unfiled, so a missing key schedule can start the penalty clock.