Most paper tax returns need two or three Forever stamps to mail. A single Forever stamp only covers the first ounce of a standard letter, and a return with a few schedules almost always weighs more than that. If you’re wondering how many stamps to mail a tax return, the honest answer is to weigh the envelope first, then round up rather than down.
Stamp Count for a Standard Letter Envelope
A Forever stamp currently costs $0.78 and covers the first ounce of a standard letter-sized envelope (no larger than 6⅛ by 11½ inches and no thicker than ¼ inch). Each additional ounce adds $0.29.1U.S. Postal Service. U.S. Postal Service Recommends New Prices for July A standard letter tops out at 3.5 ounces.2USPS Postal Explorer. First-Class Mail
For a folded return in a business envelope:
- Up to 1 oz (roughly 4 to 5 pages): 1 stamp covers the $0.78 postage.
- Up to 2 oz (roughly 10 pages): 2 stamps cover the $1.07 postage.
- Up to 3 oz (roughly 15 pages): 2 stamps cover the $1.36 postage.
- Up to 3.5 oz (the letter maximum): 3 stamps cover the $1.65 postage.
If your envelope is heavier than 3.5 ounces or larger than the letter dimensions above, it moves into a different price category.
Stamp Count for a Large Manila Envelope
Many filers use a 9-by-12 or 10-by-13-inch manila envelope so the forms don’t have to be folded. Anything larger than a standard letter or thicker than ¼ inch is classified by the Postal Service as a “flat” and priced higher.3USPS Postal Explorer. Sizes for Large Envelopes and Flats Large envelopes start at $1.63 for the first ounce, with each additional ounce adding roughly $0.27 to $0.28.4United States Postal Service. Notice 123 – Price List
Using Forever stamps on a manila envelope:
- Up to 2 oz: 3 stamps cover the $1.90 postage.
- Up to 3 oz: 3 stamps cover the $2.17 postage.
- Up to 4 oz: 4 stamps cover the $2.44 postage.
- Up to 6 oz: 4 stamps cover the $3.00 postage.
The manila envelope itself weighs close to an ounce empty, so factor that in. Ten pages of tax forms plus a manila envelope will usually land somewhere between two and three ounces.
Weigh It, or Overpay by One Stamp
A kitchen scale is accurate enough for this. So is a trip to the post office counter, where a clerk will weigh the envelope and tell you the exact postage. If neither is convenient, the safer move is to add one extra Forever stamp above what you think you need. Overpaying by $0.78 is nothing compared to what happens when postage is short.
Why Underpaying Is the Real Risk
Under federal law, a return is considered filed on the date it’s postmarked, not the date the IRS receives it, so an envelope postmarked April 15 counts as on time even if it arrives a week later. That rule only works if the envelope has enough postage and is properly addressed.5Office of the Law Revision Counsel. 26 USC 7502 – Timely Mailing Treated as Timely Filing and Paying
A letter mailed with no postage gets stamped “Returned for Postage” and comes back without the Postal Service attempting delivery. A letter with some postage but not enough gets marked with the deficiency, and the IRS has to pay the shortage to accept it. If they refuse, the envelope bounces back to you.6United States Postal Service. Domestic Mail Manual P011 – Payment By the time you add the missing postage and remail it, the new postmark is days or weeks past the deadline, and the IRS treats that later date as your filing date.
Mailing Close to the Deadline
If you’re dropping the return in the last day or two before April 15, take it inside the post office rather than using a curbside collection box. Boxes may not be emptied until the next morning, which puts a postmark one day late on your envelope. Ask the clerk for a hand cancellation so the date is clearly stamped on the envelope in front of you.
For 2026, April 15 falls on a Wednesday, so the deadline doesn’t shift.7Internal Revenue Service. When to File
Certified Mail if You Want Proof
Regular First-Class Mail is cheapest but comes with no tracking. Certified Mail gives you a mailing receipt with a postmark date, which is the cleanest evidence you filed on time if a dispute ever comes up. A Return Receipt adds either a signed green card ($4.40) or an electronic confirmation ($2.82) on top of the Certified fee and regular postage.8United States Postal Service. Notice 123 – Price List Priority Mail is another option: it includes USPS Tracking and up to $100 of insurance built in.9United States Postal Service. Priority Mail
Send It to the Right Address
The IRS uses different mailing addresses depending on your state and whether you’re enclosing a payment. Returns without a payment go to processing centers in Austin, Kansas City, or Ogden. Returns with a check go to lockbox addresses in Charlotte or Louisville.10Internal Revenue Service. Where to File Addresses for Taxpayers and Tax Professionals Filing Form 1040 Confirm the current address in the Form 1040 instructions before you seal the envelope. A check should be made out to “United States Treasury,” never stapled to the return, and never cash.11Internal Revenue Service. Form 1040-V, Payment Voucher for Individuals Adding a check won’t change your stamp count.
Private Carriers Are an Option, With Limits
You aren’t required to use USPS. Certain FedEx, UPS, and DHL services are designated by the IRS and qualify for the same postmark-equals-filing-date treatment. Not every service level counts. FedEx Ground and UPS Ground, for example, are not on the list.12Internal Revenue Service. Private Delivery Services (PDS) One catch: payments go to IRS P.O. boxes, and private carriers can’t deliver to P.O. boxes, so if you owe money, mail it through USPS.