HSK Writing Checker Writing guides

了 in Chinese writing: 5 mistakes learners make

了 is not a past-tense marker, and treating it like one is behind most of the 了 mistakes in HSK writing. Here are the five that come up most, and a simple rule for each.

Updated 14 November 2026

Chinese has two common uses of 了. After a verb, it says an action was completed (我买了一本书). At the end of a sentence, it says a situation has changed (下雨了, "it has started raining"). Most mistakes come from adding 了 just because something is in the past.

1. Adding 了 to habits and repeated actions

去年我每天都跑步了。

去年我每天都跑步。

Something you did regularly is not one completed action. With 每天, 常常, 经常 or 总是, leave 了 out. The time word (去年) already tells the reader it was in the past.

2. Adding 了 to describe a past state

小时候我很胖了。

小时候我很胖。

Describing what something was like in the past does not need 了. Adding it at the end would mean "I have become fat", a change, which is not what you mean.

3. Using 了 after verbs like 喜欢, 是 and 觉得

那时候我觉得了汉语很难。

那时候我觉得汉语很难。

Verbs of feeling, thinking and being (喜欢, 觉得, 认为, 是, 在) describe states, not actions that finish, so they normally do not take 了 straight after them.

4. Putting 了 in the wrong place with a duration or number

我在北京住两年了半。

我在北京住了两年半。

With an amount of time or a number of things, 了 goes right after the verb: verb + 了 + amount. If you also add 了 at the end (我在北京住了两年半了), it means you still live there.

5. Forgetting 了 for a completed action with a number

昨天我买三本书。

昨天我买了三本书。

The opposite mistake: when a single action was completed and you say how much or how many, Chinese needs 了 after the verb. A time word like 昨天 alone is not enough here.

A quick test before you add 了

These rules cover the cases that cost marks most often. Chinese speakers also leave 了 out in places where the meaning is already clear, so if you are unsure in a long story, check one or two sentences rather than adding 了 everywhere.