Lemons will typically last up to 4 weeks in the refrigerator before they go bad and need thrown out.
If you leave the lemons out of the fridge they typically only last around 1 week before they start to go bad and shrivel up.
You should eat the lemons before the 4 weeks if you want them to be fresh and taste good though.
After 4 weeks in the fridge the lemons should be thrown out since they'll no longer be any good.
However if you want to keep the lemons good longer you should freeze them.
Lemons will last for up to 4 months in the freezer so if you want to keep the lemons longer then freeze them.