同学你好，该知识点来自沪江网校《英语零基础直达大学六级【7月班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好~
It has been estimated that的时态是现在完成时。
这里强调事件已经发生，即已经有某种预测，而且和现在有一定联系，即可能对现在造成某种影响，比如
It has been estimated that most people in their 20s who had college degrees were not in jobs that required them: another sign that we are pushing kids into college who will not get much out of it but debt.
据估计，在拥有大学学位的20多岁的人当中，大多数人并未从事与专业相关的工作。这也表明了我们在把孩子们推进大学，而他们除了债务却几无所得。

It is estimated that 时态是一般现在时。
这里仅仅说明有这种预测，这是一种现在的状态，不强调这种预测是之前已经完成的
It is estimated that the meeting will last four days.
这次会议预计要开4天。


祝同学学习进步~