Quick answer: Yes. An ordinary Forever stamp can pay postage on a qualifying domestic postcard. At current rates it has an 82-cent value while the domestic postcard rate is 65 cents, so you would overpay by 17 cents. A postcard-rate stamp is the closer match.
Which stamp should you use?
| Mailpiece | Current rate | Practical choice |
|---|---|---|
| Qualifying domestic postcard | $0.65 | Postcard-rate stamp |
| Domestic postcard with an ordinary Forever stamp | $0.82 paid | Accepted value, but overpays |
| Qualifying international postcard | $1.75 | One Global Forever stamp |
The Card Still Has to Qualify as a Postcard
For USPS postcard pricing, the finished card must be rectangular and at least 5 inches long, 3-1/2 inches high, and 0.007 inch thick, but no more than 6 inches long, 4-1/4 inches high, and 0.016 inch thick. An oversized, unusually thick, folded, or nonrectangular card may be priced as a letter or another mailpiece even if a postcard stamp is attached.
Measure the finished piece rather than the package label. A greeting card mailed in an envelope is ordinarily evaluated as a letter, not as a postcard.
Domestic and international postcards are different
The 65-cent price is for a qualifying domestic postcard. A postcard sent outside the United States uses the international postcard rate. For a qualifying international postcard, one Global Forever stamp currently covers the $1.75 rate.
See Are Postcard Stamps Forever? for how postcard stamps retain their designated rate value, or return to the Forever stamps FAQ.
Sources checked: USPS domestic letter and postcard guide and USPS First-Class Mail International. Rates can change; verify before mailing.