The Postal Service said Thursday that most rates will increase April 17 under a formula that allows the agency to raise prices within the rate of inflation.

The post office said the 44-cent price of a first-class stamp won’t change, but heavier letters will cost more. The basic rate is for the first ounce, and the price for each extra ounce will rise from 17 cents to 20 cents.

"While changing prices is always a difficult decision, we have made every effort to keep the impact minimal for consumers and customers doing business with us at retail lobbies," Postmaster General Patrick R. Donahoe said in a statement.

The post office can raise rates as long as it doesn’t exceed inflation, which would permit an increase of 1.7 percent averaged over all mail.

The Postal Service lost $8.5 billion last year despite cuts of more than 100,000 jobs and other reductions in recent years.

The agency has lost considerable business to the Internet. Last summer the post office sought an increase that would have exceeded inflation, citing the unusual business conditions of the recession. That was rejected by the independent Postal Regulatory Commission.

The post office has appealed. In the meantime it is moving to increase rates within the legal limit because of the urgency of its financial condition.

Its filing with the Postal Regulatory Commission also said the agency expects to raise rates annually in mid-April. The last rate increase was in May 2009.

Other decisions on rates included:

— Post cards will rise by a penny to 29 cents.

— Letters to Canada or Mexico increase to 80 cents, from 75 cents to Canada and 79 cents to Mexico.

— Letters to other international destinations will remain unchanged at 98 cents.

— Express Mail and Priority Mail prices are not affected.

—There will be a variety of price changes for other mailing services, including advertising mail, periodicals and packages.

The Postal Service does not receive tax dollars for its operations.

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Online: http://www.usps.com/prices

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