NEW YORK — The price of a first-class stamp is set to jump again next month, meaning you might want to stock up on Forever stamps now. On May 11, a first-class stamp will go up by 2 cents to 44 cents. Other rates are set to rise as well. The post office adjusts rates each May, but any increases must be at or below the rate of inflation under a 2006 law. Still, there have been more price hikes — six including the one next month — this decade than any other. Consider the arc of stamp prices over the years. In 1958, a first-class stamp cost 4 cents. It was 15 cents by 1978, and 32 cents in 1998. The Forever stamp made its debut in 2007, when it cost 41 cents. A Forever stamp costs the same as a regular stamp, but can be used to mail letters at any time in the future regardless of how much prices go up. Some might feel stocking up on Forever stamps now is a smart bet, with the postal service staring down some major financial challenges. Postmaster General John Potter last month sought permission from Congress to cut mail delivery to five days a week, saying the post office will run out of money this year unless it gets help. The agency lost $2.8 billion last year and is looking at much steeper losses this year. Any price hike is bound to provoke some complaints, but the bump won’t amount to a significant hit if you don’t use the mail often. “For an average household, the change will amount to $3 extra over the course of the year,” said Yvonne Yoerger, a spokeswoman for the United States Postal Service. Still, Yoerger says it can’t hurt to stock up on Forever stamps before the pending jump. At the very least, they’ll cut out the need to attach any pesky 1- or 2-cent stamps with old stamps. Other rates set to rise on May 11: • A postcard stamp will be 28 cents, up from 27 cents • The first ounce of a large envelope will be 88 cents, up from 83 cents • The first ounce of parcel post will be $1.22, up from $1.17 • The first ounce of first-class mail to Canada will be 75 cents, up from 72 cents • The first ounce of first-class mail to Mexico will be 79 cents, up from 72 cents • The first ounce of all other international first-class mail will be 98 cents, up from 94 cents