估计 / 可能
Similarities
Both 估计 and 可能 express an inference based on the situation or the information available.
今天的工作估计完不成了，因为出了点儿问题
今天的工作可能完不成了，因为出了点儿问题
Either word works in this sentence.
1. 估计 is a verb, 可能 a modal verb
估计 + Clause
可能 + Verb
明天就可以上网查成绩了，我估计这次考试考得不错
明天就可以上网查成绩了，我这次考试可能考得不错
估计 can serve as the predicate itself and take a whole clause after it.
可能 normally sits in front of the main verb.
2. 可能 can also be an adjective
他这么多天没来上课，最可能的原因就是他回国了
As an adjective 可能 means “possible”, “likely”. 估计 cannot be used this way.
3. 很可能
很可能他还不知道这件事
他很可能还不知道这件事
可能 takes 很 in front of it: 很可能. 很估计 is simply wrong.
Which one when?
我估计他已经到了
他可能已经到了
| 估计 | 可能 |
|---|---|
| A verb | A modal verb or an adjective |
| Can introduce a whole clause | Sits before the verb |
| The speaker's estimate | The likelihood of an event |
| 很估计 ❌ | 很可能 ✅ |
Remember:
估计 = to reckon, I'd say.
可能 = may, possibly.
很可能 is very common; 很估计 is incorrect.