You can usually tell by looking at it, or by giving it a quick feel!
How Can I Tell If A Kiwi Is Good To Eat?
Feel the kiwi gently in your hand, and give it a light squeeze. It should be relatively firm. However, if it's softer than you'd expect, it's probably still safe to eat - it just might taste a bit sweeter!
See if your kiwi is wet on the outside - ideally, it should be completely dry. If there are any leaky patches in the skin, then it's probably started to rot, so you'd do best to throw it out before it starts attracting insects!
Check for bruising, prune-like skin and discoloration. All of these are signs that the fruit might be over-ripe.