Potato salad will never be as good as when it was first made. Use it within a day or two. Depending on what you put in your potato salad will depend on how long your salad will last. If you put eggs in your salad then you have 3 days to use it up in. If you omit the eggs then you have about 5 days as long as the salad doesn't sit out and get warm since it has mayonnaise in it.