To express period and frequency—in other words, to say how many times something happened per day, week, and year, and so on—we need the a counter with the target particle. See here for an introduction to counters in Japanese.
This structure is most often used with the counter 回, which means “times” (e.g. I go back to my hometown 3 times per year”).
|Five times per week.
|To return to your hometown twice per year.
|To read 3 books per week.
Note the position of the object particle—before the counter.
In fact, the target particle is often omitted.
|To go to the gym four times per week.
|To go abroad twice per year.