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
Postcard pricing depends on the finished card meeting USPS size, shape, thickness, and preparation rules. An oversized, unusually thick, folded, or nonrectangular card may be priced as a letter or another mailpiece even if a postcard stamp is attached.
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.