This research aimed to determine the effect of different harvest times representing 12 months of a year on the herba and leaf yields, leaves essential oil content and composition, extract of total phenols by the Folin–Ciocalteu colorimetric method, phenolic components, antioxidant activities according to Free radical scavenging activity DPPH and ferric ion reducing antioxidant power (FRAP) methods in common sage (Salvia officinalis L.). Fresh herb yield between 500.0 and 961.0 kg/da, dry herb yield between 223.4 and 556.6 kg/da, dry leaf yield between 129.6 and 367.2 kg/da, essential oil content between 0.83 and 3.33%, total phenolics between 14.54 and 30.83 mg/g were changed in common sage during the harvest periods of growing season. Herb and leaf yields, essential oil contents and yields, and total phenolics were found higher in the summer and autumn harvests in comparison to the winter and spring harvests. The main components of common sage essential oil were 1,8‐cineole (11.93‐31.87 %), α‐thujone (15.72‐26.26%), β‐thujone (4.51‐27.67%), and camphor (3.65‐23.02%). While the ratios of 1,8‐sineol and camphor of the common sage leaves essential oil were the least in spring season, the ratios of α and β‐thujone were the highest in the same season. The most important phenolic compounds in the common sage extracts were rosmarinic acid (15.15‐100.57 mg/g), naringin (9.59‐41.81 mg/g), hesperidin (9.80‐53.26 mg/g), and rutin (0.73‐10.04 mg/g). The highest antioxidant activities of the leaves were found in the plants harvested in May and June, and the lowest antioxidant activities of the the leaves were found in the plants harvested in March and April.