WASHINGTON — An extra penny for your thoughts.

Mailing a letter costs a penny more this week, with the price of a first-class stamp rising to 42 cents Monday.

But folks who planned ahead and bought Forever stamps for 41 cents each can still use them without extra postage.

Sorry, Forever stamps also went up to 42 cents. But buyers may want to stock up anyway, looking ahead to next May when prices are expected to be adjusted again.

The cost to mail a post card will also went up a penny, to 27 cents.

Other new rates:

—Large envelope, 2 ounces, $1, up 3 cents.

—Certified mail, $2.70, up 5 cents.

—First-class international letter to Canada or Mexico, 72 cents, up 3 cents.

—First-class international letter to other countries, 94 cents, up 4 cents.

—Priority mail flat-rate envelope, $4.75, up 25 cents.

—Express mail flat-rate envelope, $16.50, up 25 cents.

Postage rates last went up in May 2007, with a first-class stamp jumping 2 cents to 41 cents.