A Forever stamp is designed to cover the current one-ounce First-Class Mail letter rate, but that does not mean every envelope needs exactly one stamp. Weight, shape, thickness, rigidity, and optional mailing services can all change the postage required. The safest approach is to check the finished mailpiece before you add postage.
As of September 3, 2026, USPS lists the Forever stamp value at 82 cents. USPS also states that letters over one ounce need additional postage, with each additional ounce currently priced at 29 cents for letters up to 3.5 ounces. Because postal rates can change, use current USPS information when you are ready to mail rather than treating any article as a permanent rate chart.
What one Forever stamp covers
For a standard qualifying First-Class Mail letter weighing up to one ounce, one Forever stamp covers the current letter rate. A Forever stamp remains usable for that one-ounce rate even if the price of a new Forever stamp changes later.
If you want a broader explanation of how this stamp type works, start with Understanding USPS Forever Stamps. For the current official rate and mailing rules, check the USPS website before sending.
Four reasons one stamp may not be enough
1. The finished letter weighs more than one ounce
Cards, multiple sheets of paper, invitations, inserts, photos, and heavier envelopes can push a mailpiece beyond one ounce. USPS currently allows letter pricing up to 3.5 ounces, with an additional-ounce charge for each extra ounce or fraction that requires it. Weigh the complete, sealed envelope rather than estimating from the contents alone.
2. The envelope is nonmachinable
USPS notes that letters with characteristics such as unusual rigidity, lumps, clasps, string, buttons, or certain square or vertical shapes can require a nonmachinable surcharge. The current USPS consumer guide lists that extra charge as 49 cents. This is a good reason to check the shape and flexibility of a finished invitation or specialty card before mailing it.
3. The mailpiece belongs in a different size category
A large envelope, very thick mailpiece, or package can fall under different pricing rules. Adding more Forever stamps does not automatically turn an oversized or package-shaped item into a correctly paid standard letter. If the dimensions or thickness seem outside normal letter proportions, measure the mailpiece and use the current USPS price calculator or ask at a Post Office.
4. You are adding an optional service
Services beyond ordinary First-Class Mail postage can cost extra. If you need a service such as Certified Mail or another add-on, calculate the full required postage instead of assuming the base stamp covers everything.
A simple pre-mail checklist
A repeatable check can prevent both underpaying and unnecessary overpaying:
- Finish the envelope completely, including every insert.
- Weigh the sealed mailpiece.
- Check its dimensions, thickness, shape, and flexibility.
- Decide whether you need any optional USPS service.
- Use the current USPS rate information or postage calculator.
- Add postage only after you know the required amount.
This matters especially for invitations and layered cards. The ShadowsDeal guide on choosing Forever stamps for wedding invitations also recommends evaluating the finished envelope rather than guessing from the card alone.
Why adding another Forever stamp is not always the cleanest answer
You can use multiple valid stamps to meet a postage amount, but using another full Forever stamp may add more postage than necessary when the shortfall is only an additional-ounce or nonmachinable charge. Exact additional-postage denominations or a USPS-calculated amount can make the total easier to match.
Once you know what your regular mail needs, you can browse All Forever Stamps or the booklets, panes, and sheets collection for standard postage options. Those store collections are shopping resources, not substitutes for USPS rate determination.
FAQ
Can I use more than one Forever stamp on a letter?
Yes, valid stamps can be combined toward the postage due. However, calculate the required postage first so you do not add more value than you need.
Does a square envelope automatically need more postage?
USPS identifies square and some other unusual letter shapes as potentially nonmachinable, which can require an additional charge. Check the current USPS requirements for the exact envelope you are mailing.
How do I know whether my envelope is over one ounce?
Weigh the fully assembled and sealed envelope. If you do not have a suitable scale, a Post Office can help determine the required postage.
Is ShadowsDeal the Postal Service?
No. ShadowsDeal is an independent reseller and is not affiliated with or endorsed by the U.S. Postal Service. You can review the store's Independent Reseller Notice for that disclosure.
Bottom line
One Forever stamp is a useful starting point for a standard one-ounce letter, not a universal answer for every envelope. Weight the finished mailpiece, check its shape and thickness, and verify current USPS pricing before mailing. Once the postage requirement is clear, choose the stamp format that fits your routine without guessing.