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

The cash-strapped U.S. Postal Service announced today 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 rate increase will make only a small dent in those losses, caused by the recession, movement of mail to the Internet, and a requirement that the agency fund future retiree medical benefits years in advance.

Other proposals to cut the losses have included reduction of mail delivery from six to five days a week and closing thousands of offices across the country.