Adverbs of Frequency

Adverbs of Frequency are adverbs of time that answer the question "How frequently?" or "How often?". They tell us how often something happens. Here are some examples:

1. daily, weekly, yearly
2. often, sometimes, rarely

You probably see a difference between a) and b) above. With words like daily  we know exactly how often. The words in a) describe definite  frequency. On the other hand, words like often  give us an idea about frequency but they don't tell us exactly. The words in b) describe indefinite frequency.

We separate them into two groups because they normally go in different positions in the sentence.

Adverbs of Definite Frequency

Examples:

• hourly, daily, weekly, monthly, yearly
• every second, once a minute, twice a year
• once, twice, once or twice, three times

Adverbs of definite frequency, like all adverbs of definite time, typically go in END position. Look at these examples:

• Most companies pay taxes yearly.
• The manager checks the toilets every hour.
• The directors meet weekly  to review progress.

Sometimes, usually for reasons of emphasis or style, some adverbs of definite frequency may go at the FRONT, for example:

• Every day, more than five thousand people die on our roads.

Adverbs of Indefinite Frequency

Look at these examples of adverbs of indefinite frequency:

Adverbs of indefinite frequency mainly go in MID position in the sentence. They go before  the main verb (except the main verb "to be"):

• We usually  go shopping on Saturday.
• I have often  done that.
• She is always late.

Occasionally, sometimes, often, frequently and usually  can also go at the beginning or end of a sentence:

• Sometimes  they come and stay with us.
• I play tennis occasionally.

Rarely and seldom  can also go at the end of a sentence (often with "very"):

• We see them rarely.
• John eats meat very seldom.

sources : Original Link