In Bree, Year 1 corresponded to T.A. 1300, however the Shire-reckoning counted as Year 1 the year that colonization of the Shire began by the Bree-hobbits Marcho and Blanco. Therefore, years of the Third Age can be converted to Shire-years by subtracting 1600.
The last year of the Third Age was year S.R. 1421. In the New Reckoning of King Elessar, the year 1 of the Fourth Age the year began on March 25, old style. The Hobbits mostly ignored the change and so for them Fo.A. 1 was just 1422.
 See also