When storing homemade garlic butter in the fridge the homemade garlic butter will last for up to 15 days in the fridge.
When you do store homemade garlic butter in the fridge be sure to place the homemade garlic butter in an airtight container before refrigerating it.
Keep the homemade garlic butter sealed in the airtight container when not using it and keep it refrigerated.
If you do that then the homemade garlic butter will last up to 15 days before it goes bad.
it's best to eat or use the homemade garlic butter before the 15 days though because the longer the homemade garlic butter remains in the fridge the less fresh it becomes.
So it may not be as enjoyable as it was when fresh but it will remain safe to eat.
If you've had the homemade garlic butter in the fridge longer than 15 days then it's likely bad and should probably be thrown out.