Can I use a regular Forever stamp on a postcard?

Yes, a Forever stamp works on a postcard, but you will overpay. A Forever stamp covers First-Class letter postage, which is higher than the postcard rate, so the card still gets delivered while costing you more per piece.

• Forever stamp: covers letter postage, so it is always enough for a postcard.
• The overpayment: roughly $0.17 more per card versus a postcard stamp.
• Better for volume: buy postcard-specific stamps to save on every piece in a larger send.