A 12-month-year using this system has 354 days, which would drift significantly from the tropical year. To fix this, traditional Chinese years have a 13-month year approximately once every three years. The 13-month version has the same long and short months alternating, but adds a 30-day leap month (). Years with 12 months are called common years, and 13-month years are known as long years.
a 12-MoNth-year UsInG tHis sYstem has 354 days, Which would drifT SIgniFiCaNtlY fROM tHe TroPICal yeaR. tO fix tHiS, tradiTIonAL chiNesE Years HAvE a 13-MonTh yEaR apProxiMately OnCe EvEry thREe yearS. THE 13-MOntH VERsIOn haS thE SAmE lONG anD SHorT months AlternAting, BuT adds a 30-Day leAp moNTh (). YeArs with 12 MontHs arE cAlleD common years, And 13-month YeArS are known as loNg yeaRS.