Yes, you can use Forever stamps on postcards, and USPS will deliver the card without issue. The catch is price: a Forever stamp is worth $0.78, while the domestic postcard rate is only $0.61, so every Forever stamp you stick on a postcard overpays by $0.17.1USPS. First-Class Mail For one card, it’s nothing. For a stack, it adds up.
The $0.17 Overpayment
A Forever stamp is tied to the current First-Class Mail 1-ounce letter rate of $0.78, not the postcard rate of $0.61.1USPS. First-Class Mail USPS does not refund overpaid postage once a stamp is on a mailed piece. Their refund rules cover exchanges of full, unused panes or coils only.2Postal Explorer. 604 Postage Payment Methods and Refunds
Mail one postcard from vacation and the $0.17 gap doesn’t register. Mail 100 wedding save-the-dates or business announcements and you’ve thrown away $17.
Cheaper Ways to Pay Postcard Postage
USPS sells stamps denominated at the $0.61 postcard rate at post office counters and through its online store.3USPS. Stamps – Postcard These come in various designs and work the same way Forever stamps do, covering the current postcard rate whenever you use them.
If you have leftover stamps from previous rate changes, you can combine lower-denomination stamps to hit $0.61 exactly. USPS sells values as low as 1¢ and 4¢.4USPS.com. The Postal Store – Stamps It works, but it turns mailing a postcard into a small project.
When One Forever Stamp Isn’t Enough
A single Forever stamp covers any standard rectangular postcard. A few situations push the required postage above $0.78, and slapping one Forever stamp on the card will get it returned for more postage or held up in delivery.
- Square postcards fail the aspect ratio rule and are classified as nonmachinable letters. The nonmachinable surcharge is $0.49 on top of the letter rate, bringing the total to $1.27. One Forever stamp leaves you $0.49 short.5Postal Explorer. Notice 123 – January 2026 Price Change
- Cards larger than 6-1/8 inches high or 11.5 inches long cross into large envelope pricing, which runs higher still.6Postal Explorer. Sizes for Letters
- Anything with clasps, buttons, string, or uneven surfaces gets flagged as nonmachinable and triggers the same $0.49 surcharge.7Postal Explorer. 201 Quick Service Guide
What Counts as a Postcard for Postage
The $0.61 rate only applies if your card fits inside a specific rectangle. To qualify, the postcard must be:8Postal Explorer. Sizes for Postcards
- At least 3.5 inches high, 5 inches long, and 0.007 inches thick
- No more than 6 inches high, 9 inches long, and 0.016 inches thick
- Rectangular, with a length-to-height ratio between 1.3 and 2.5
Privately produced postcards can go all the way up to 6 × 9 inches and still qualify for card pricing under the USPS Domestic Mail Manual.9Postal Explorer. DMM 201 Physical Standards Many people assume the ceiling is 4.25 × 6 inches because that’s the limit for USPS-printed stamped cards, and some simplified guides only mention the smaller size. Exceed the maximum entirely and USPS reclassifies your card as a letter, with letter-rate postage.8Postal Explorer. Sizes for Postcards
International Postcards Need More Postage
A domestic Forever stamp does not cover an international postcard. The international rate is $1.70 to any country.10USPS. First-Class Mail International A Global Forever stamp covers a 1-ounce letter or postcard worldwide and, like the domestic version, never expires.
You can also combine domestic stamps to reach $1.70. Two Forever stamps come to $1.56, which falls $0.14 short. Three Forever stamps total $2.34, which works but wastes $0.64. Pairing one or two Forever stamps with lower-denomination stamps closes the gap more efficiently.11USPS.com. How to Send a Letter or Postcard: International
International postcards must be rectangular, 5.5 to 6 inches long, 3.5 to 4.25 inches high, and no more than 0.016 inches thick. Write “AIRMAIL/PAR AVION” on the address side.11USPS.com. How to Send a Letter or Postcard: International
The Short Version
If you already have Forever stamps and just want to send a postcard or two, use them. Delivery is guaranteed and the $0.17 loss is trivial. If you send postcards in any quantity, buy a sheet of $0.61 postcard stamps and save the Forever stamps for letters.