No. You cannot mail your federal and state tax returns together. The IRS and your state tax department are separate agencies with separate processing centers, so each return needs its own envelope addressed to its own agency. Put both in one envelope and one of them will never reach the right place.
Why One Envelope Won’t Work
The IRS handles your federal Form 1040. Your state’s department of revenue handles your state return. Neither agency forwards mail to the other. If your state return lands at an IRS processing center, it isn’t rerouted; it’s set aside or discarded, and your state treats the return as unfiled. Penalties and interest start running from the state deadline forward, and you may not learn about the problem until a notice arrives months later.
Prepare two mailings. One envelope goes to the IRS processing center assigned to your state. The other goes to your state tax department. If you owe money to both, write two separate checks and put one in each envelope.
Where to Send the Federal Return
The IRS address for a paper Form 1040 depends on two things: the state you live in and whether you’re enclosing a payment. Returns with a check go to a different address than returns expecting a refund. The IRS publishes the full table each filing season on its website.1Internal Revenue Service. Where to File Paper Tax Returns With or Without a Payment Look it up fresh rather than reusing an address from last year, because processing centers do get reassigned.
If you owe a balance, include Form 1040-V with your check or money order. Make the payment out to “United States Treasury,” and write your Social Security number and “2025 Form 1040” on the check itself. Don’t staple the check or voucher to the return; leave everything loose inside the envelope.2Internal Revenue Service. Form 1040-V Payment Voucher for Individuals Never send cash. And sign the return. An unsigned return is treated as unfiled, and on a joint return both spouses have to sign.3Internal Revenue Service. Taxpayer Signature
Where to Send the State Return
Each state publishes its own mailing addresses, and most states, like the IRS, use one address for returns with a payment and a different one for returns claiming a refund. Check the instruction booklet your state forms came with, or your state tax department’s website, for the correct address.
A handful of states have no individual income tax, so if you live in one of those you have no state return to mail in the first place. Most state deadlines line up with the federal April 15 date, but a few don’t. Confirm your state’s due date rather than assuming it mirrors the federal one. The federal deadline for tax year 2025 is Wednesday, April 15, 2026.
The Postmark Counts, Not the Delivery Date
Your return doesn’t have to arrive at the IRS by April 15. It has to be mailed by April 15. Federal law treats the postmark on the envelope as the filing date, so a return postmarked April 15 and delivered April 20 still counts as timely.4Office of the Law Revision Counsel. 26 USC 7502 – Timely Mailing Treated as Timely Filing and Paying The same rule applies to any payment enclosed.
Two conditions have to be met. The postmark must fall on or before the deadline, and the envelope must be properly addressed with enough postage. A meter stamp from an office machine qualifies, but if you’re mailing on the last day, get a hand-stamped postmark at the post office counter to remove any doubt.
Certified mail is worth the few extra dollars near the deadline. The date on the certified mail receipt is treated as the postmark date, and the receipt itself is your evidence that you mailed the return.4Office of the Law Revision Counsel. 26 USC 7502 – Timely Mailing Treated as Timely Filing and Paying If the IRS ever claims your return arrived late, that receipt is the proof that resolves it.
If You’re Using FedEx, UPS, or DHL Instead
The postmark rule normally applies only to USPS mail, but the IRS designates certain private carrier services whose recorded ship dates count the same way.5Internal Revenue Service. Private Delivery Services (PDS) Only specific service tiers qualify:
- FedEx: First Overnight, Priority Overnight, Standard Overnight, 2 Day, and several international options.
- 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 tiers.
- DHL Express: Express 9:00, 10:30, and 12:00, plus Worldwide, Envelope, and several Import Express services.
Standard ground shipping through any of these carriers does not qualify. If you pick a service level that isn’t on the IRS list, the filing date is the date the IRS actually receives the package, not the date you shipped it. Check the current list before choosing a service.5Internal Revenue Service. Private Delivery Services (PDS)
If You Can’t File by April 15
Form 4868 buys you an automatic six-month extension, moving the filing deadline to October 15, 2026.6Internal Revenue Service. Form 4868 – Application for Automatic Extension of Time to File US Individual Income Tax Return You can file the form on paper or electronically. Making an electronic payment toward your estimated balance by April 15 also triggers an extension automatically, with no separate form to file.
The catch: an extension gives you more time to file, not more time to pay.6Internal Revenue Service. Form 4868 – Application for Automatic Extension of Time to File US Individual Income Tax Return Whatever tax you owe is still due April 15. File in October without having paid in April and you’ll owe interest and a late-payment penalty running back to the original deadline. Estimate what you owe and send a payment with the extension to hold that damage down.
Many states honor a federal extension automatically, but not all do. Check your state’s rules.
What It Costs to Be Late
Missing the filing deadline triggers two penalties that run in parallel, plus interest.
The late-filing penalty is 5% of the unpaid tax per month or partial month, capped at 25%.7Office of the Law Revision Counsel. 26 USC 6651 – Failure to File Tax Return or to Pay Tax If the return is more than 60 days late, the minimum penalty is $525 for returns due in 2026, or 100% of the unpaid tax, whichever is smaller.
The late-payment penalty is 0.5% of the unpaid tax per month, also capped at 25%.7Office of the Law Revision Counsel. 26 USC 6651 – Failure to File Tax Return or to Pay Tax In any month where both penalties apply, the filing penalty is reduced to 4.5%, so the combined charge is 5% per month rather than 5.5%. Interest also runs on the unpaid tax, compounded daily. The underpayment interest rate for the quarter beginning April 1, 2026, is 6%.8Internal Revenue Service. Internal Revenue Bulletin 2026-8
If April 15 is coming and the return isn’t ready, file the extension. It eliminates the 5%-per-month filing penalty entirely and leaves you with only the smaller payment penalty and interest on whatever balance remains.