自…之日起
from the day (that) …; with effect from
Structure
自 事件／日期 之日起 （， 时间段 内／后）
What it means
From the day that…; with effect from. The language of laws, contracts and official notices: 自 is a written 从 and 之日 a written 的那一天.
How it is built
自 + event／date + 之日起（，time span + 内／后）: 这张会员卡自购买之日起一年内有效 (This membership card is valid for one year from the date of purchase). The event can be a whole clause.
When to use it
Formal and legal; common follow-ups are 三十日内, 一年内有效, 施行, 生效 (本规定自发布之日起施行). In speech say 从…那天起.
Watch out
Don't mix 的 with 日: ✗自收到申请的日起 ✓自收到申请之日起, or 从收到申请的那天起. Don't confuse it with 截至 (lesson 5-22), which marks the end point, not the start.
Examples
自婚姻登记机关收到离婚申请之日起三十日内，任何一方都可以撤回申请。
Within thirty days from the day the marriage registry receives the application, either party may withdraw it.
本规定自发布之日起施行。
These rules take effect from the day they are published.
这张会员卡自购买之日起一年内有效。
This membership card is valid for one year from the date of purchase.
Learn this in Lesson 152 · HSK 7–9: 离婚冷静期 (The divorce cooling-off period)
A dialogue, a reading, word cards with audio and a drill that uses it, in Learn Chinese with Bao. The first lessons of every level are free.
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