"It depends on your life!". I can confidently tell you three is the lowest number I would recommend. When the same bra is worn day after day, the elastic doesn't have a long enough rest period to recover. This means a shorter life for your bra. You can wear the same bra day after day and year after year but it isn't going to be performing it's best. Bras wear out. Depending on how you care for them it's usually six months to a year. I have some bras much older because I don't wear them very often. Recently, I wore one of those bras and tossed it after the day. It was shot!