Mine are probably going to last at least 18 months. I have seven Fruit of the Loom style 9292 bras 'cause they're relatively inexpensive underwires with strech cups. They are all different colors, and took several months to find all of them in one of the two sizes I wear. White, black, red, white with red stripes, beigh, white with blue polka-dots, grey with red polka-dots.
And unless I'm doing a lot of work outside I wear them a couple days each.