How To Know When To Turn A Casual Relationship Into A Serious One

How do I know when it's time to turn a casual relationship into a serious one?

You both know when it's time to turn a casual relationship into a more serious relationship. It's something that nobody says; you just know. It happens. You end up spending more time together than when your relationship first started. You end up having more in common. That's what a serious relationship is all about.