In Bree, Year 1 corresponded to T.A. 1300, however the Shire-reckoning Year 1 corresponded to T.A. 1601: 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 Fo.A. 1 began on March 25, old style. The Hobbits mostly ignored the change and so for them the first year of the Fourth Age was just S.R. 1422.