Originally Posted by tmm99
Once opened, less than a week. You can extend the freshness by putting the tofu in another container (with a lid) and changing the water (enough water to cover the whole tofu) every day.
If I discarded tofu a week after opening, I'd throw out more than I eat. YMMV, but I have frequently cooked and eaten tofu two weeks or more after opening the package (and the package might well have been sitting in the refrigerator for a while before I opened it, too). I didn't put a lid on the container, I didn't change the water daily, and I experienced no ill effects of any kind.
If you don't like the idea of eating tofu that's been opened that long, it's possible to freeze it. I don't like frozen tofu, because freezing changes the texture as ice crystals form, but if that doesn't bother you, it's an alternative to letting it sit around until you feel like stir fry for dinner.