WASHINGTON — It’ll cost a penny more to mail a letter next year.

The cash-strapped U.S. Postal Service announced Tuesday that it will increase postage rates on Jan. 22, including a 1-cent increase in the cost of first-class mail, to 45 cents.

Under the law the post office cannot raise prices more than the rate of inflation, which is 2.1 percent, unless it gets special permission from the independent Postal Regulatory Commission. The PRC last year turned down such a request.

The post office lost $8 billion in fiscal 2010 and the bottom line is likely to be even worse when final figures for fiscal 2011 are released next month.

The current 44-cent rate has been in effect since May 2009.

While the price for the first ounce of a first-class letter will rise to 45 cents, the cost for each additional ounce will remain at the current 20 cents.

Other prices will also change including:

n Postcards will go up 3 cents to 32 cents.

n Letters to Canada and Mexico will increase a nickel to 85 cents.

n Letters to other foreign countries will go up 7 cents to $1.05.

n Prices for advertising mail, periodicals and parcels also will rise about 2.1 percent.