how often指“每隔多久,多久一次做。”，主要用来对频度副词或状语(如：once a day, three times a week 等)提问。
如：A：How often does he come here? 他(每隔)多久来一次?B：Once a month. 每月一次。
A：How often do you visit your mother? 你多长时间看你妈妈一次?B：Once a week. 一周一次。
how often用来提问某动作或状态发生的频率，对“一段时间内发生了几次活动”（always，usually， often， never或twice a day等表示频度的词或短语）提问时用；
eg:How often do his parents let him watch TV?他父母多久让他看一次电视？
对于how often 的句型回答，一般有这些词表示频率：once,twice,three times,four times,everyday等等。
【扩展资料】
大家学习了always, usually, often, sometimes, never等表示时间频度的副词。这些词通常用来说明在一段时间内做某事的多少或某种状态存在的次数的多少。例如：
We usually get up at half past six. 我们通常六点半起床。
Sometimes he goes to see his grandpa on weekends. 周末，他有时候去看望爷爷。
但是，在日常生活中一流范文网，我们不可能总是用陈述句来表达自己的或他人的一些行动，或者事物所存在的状态。我们还要向对方提出一些问题，请求对方回答。在这种情况下，我们还要用疑问句。请看下面几组对话：
1. —How often do you play football?
—I usually play football after school.
2. —How often does Mary go to the concert?
—She often goes to it on Saturday evening.
3.—How often does my daughter take the medicine?
—Three times a day.
不知大家是否注意到，我们针对上面所说的频度副词和表示“在某段时间内某种动作的次数”的状语提问时，都要用how often。
换句话说oftenoften，如果要回答由how often提问的句子， ? ?我们通常要用频度副词或诸如every day, each week, once a week, twice a day, four times a month等来回答。例如：
4. —How often do you borrow books from the library?
—Twice a month.
5. —How often does your mother do the washing?
—She does it every day.
6. —How often can you go to the movie?
—Once a week.
在大家所做的练习中，常见的有“句型转换”。这种题型有一种“就划线部分提问”，要求针对陈述句中的划线部分提出问题（也就是把陈述句变成特殊疑问句），其中就有针对上面所说的频度副词或every day, each week, once a week, twice a day, four times a month等提问的句子。这时候自然要用how often来提问了。例如：
Jack watches TV three times a week. →How often does Jack watch TV?? ?Our school has a sports meeting twice a year. →How often does your school have a sports meeting?
要注意的是，陈述句在变成这种特殊疑问句时，其结构是：How often+助动词（或系动词 be）+主语+实义动词（如果前面是系动词be的某种形式，则不再用实义动词）+其它成分？
参考资料来源搜狗指南 - zhinan.sogou.com百度文库 - wk.baidu.com
