How long does the effect of teeth whitening last?

I hadn't really paid much attention to it until recently, but I suddenly noticed it when I looked in the mirror. My teeth had faded and turned yellow compared to before. So, I suddenly started thinking about teeth whitening. I have a question.

I'm sure teeth whitening would be effective, but for some reason, I don't think the effect would last. If my teeth return to their original color after a short while, I think it would be a burden to do it repeatedly.

How long does the effect of teeth whitening last?