will作为情态动词可以表示有一定根据或理由的推测。
1.对现在情况的推测：
There is a ring at the door. That will be the postman, I suppose.
门铃响了，我想可能是邮差来了。
That’ll be my husband. He said he would phone at this time.
大概是我丈夫打来的电话，他说她这个时间要来电话的。
She will be in New York now.
此刻她可能在纽约了。
He will be at home now.他现在应该在家里。
注意：也可以用will be doing形式：
He'll be expecting me. 他会等着我的。
You will be deceiving yourself. 你会自欺欺人的。
It will be snowing now in He Fei？
现在合肥可能正在下雪吧？
It’s 12 o’clock. He won’t be working now.
十二点了，他现在不会正在工作。
That will have been Roland. She said he'd be back at 7.
准是罗兰，她说她7点钟回来。
2. 对将来情况的推测：
It will snow tomorrow.
明天会下雪。
Let’s not go shopping today. The shop will be crowded.
我们今天不要去逛商店了，商店里大概很拥挤。
There will have been a definite result before Friday.
星期五以前将肯定会有结果。
3.对过去情况的推测，用will have done，主语一般是第二、第三人称。
She will have arrived by now.
她应该已经到了。
She will have forgotten her birthday.
她肯定忘记了她的生日。
The holiday will have done him the world of good.
假期定会对他大有好处。
注意：will have done用法：
will have done第一种用法：为will用作情态动词，对过去发生的事件作相当肯定的推测。will的这种用法不及must常用，但会见到，也是今天论述的重点。例如：
The light is on and the door unlocked. They will have left in a hurry. 灯没关，门也没锁。他们十有八九走得很仓促。
更常见的是用must have done. They must have left in a hurry.
will have done第二种用法即16种时态中的将来完成时态。
a. 状态已完成：表示某事持续到将来某一时为止一直有的状态。并在将来完成。
b. 动作已完成：表示将来某一时或另一个将来的动作之前，已经完成的动作或已经对动作产生一定的影响。
例：
a：They will have been married for 20 years by then. 到那时他们俩结婚就满20年了。
b: You will have reached Shanghai by this time tomorrow. 明天的这个时候你就到上海了。
will have done第三种用法表示某种状况将一直持续到说话人所提及某一将来时间。
如：We will have been married a year on June 25th.
到6月25日我们俩结婚就满1年了。
By this time next week, I will have worked for this company for 24 years.
到下星期此刻，我已经为该公司干了24年了。
4.will表示推测：表示大概，可能，其可能性较大，但把握小于must。
This will be the person you are looking for.这可能就是你要找的人。
I think you will have heard the news.我想你可能已经听到这个消息了。
表示推测，把握性比will低一些。此时用would.
I'm afraid the journey would be very boring.我担心这次旅行会很无聊。