Duration with 了

HSK 3

Structure (结构 jiégòu)

Completion: Verb了Time period. In progress: Verb了Time period了.

Use '了' with a duration of time to express how long an action has lasted, which may still be ongoing.

When talking about how long an action lasted, we use 了 with a time-duration expression. There are two main cases:

Completed action: Verb + 了 + Duration. Example: 我学了一年汉语 (I studied Chinese for one year, and no longer do so).
Ongoing action: Verb + 了 + Duration + 了. Example: 我学了一年汉语了 (I have been studying Chinese for one year, and am still studying). The second 了 at the end of the sentence is the indicator that the action is still continuing.

他学了两年中文了。
繁: 他學了兩年中文了。Tā xué le liǎng nián Zhōngwén le.
He has been studying Chinese for two years.
我等了你半个小时了。
繁: 我等了你半個小時了。Wǒ děng le nǐ bàn ge xiǎoshí le.
I have been waiting for you for half an hour.
爸爸工作了三十年了。
Bàba gōngzuò le sān shí nián le.
My father has been working for thirty years.
他们看了三个小时电视了。
繁: 他們看了三個小時電視了。Tāmen kàn le sān ge xiǎoshí diànshì le.
They have been watching TV for three hours.
我在北京住了一年。
Wǒ zài Běijīng zhù le yì nián.
I have lived in Beijing for one year.

Wrong:我学一年汉语了。
Correct:我学了一年汉语了。
There must be 了 immediately after the verb to indicate the beginning of this duration of time.
Wrong:我学了一年汉语。
Correct:我学了一年汉语了。
If the action is still ongoing, 了 must be added at the end of the sentence. Omitting final 了 means the action has concluded.