dynamic_cast overhead in C++

I know that dynamic_cast performs a runtime check and therefore is considered safer (can return null pointer on failure) but slower then static_cast. But how large is the difference in overhead between the two?

Should I really consider using static_cast in loops for performance reasons in regular large projects? Or is the difference minor and only relevant for special real-time programs?

Did you profile it?

The rule is:

• Use static_cast when you know that the target type is valid.
• Use dynamic_cast when you're not sure, and you need the program to look up the object's runtime type for you.

It's as simple as that. All other considerations are secondary.