Initially, the maximum number of days per annum for the zoyo was less than or equal to 60 for the seitei (a male between the ages of 21 and 60), 30 for the jitei (a seitei with disabilities) and the rotei (a male over age 60), and 15 days for the chunan (a male between the ages of 17 and 20), but the Kyakushiki code (a code to amend and supplement the Ritsuryo code) intended to reduce the zoyo by half was introduced in 757.
当初は正丁（21～60歳の男性）年間60日以下、次丁（正丁の障害者と老丁（61歳以上の男性））年間30日以下、中男（17～20歳の男性）年間15日以下を限度としたが、757年（天平宝字元年）に雑徭を半減する格式が出された。