FAQ 21.03 How much does it cost to call a virtual function compared to calling a normal function?

In theory, the overhead of dynamic binding is highly dependent on the compiler, operating system, and machine. In practice, almost all compilers do it the same way, and the overhead is very small.

A virtual function call typically costs 10% to 20% more than a nonvirtual function call. The overhead is smaller if there are several parameters, since the dynamic binding part of a virtual function call has constant cost. In practice, the overhead for the linkage of a function call is usually a very small percentage of the cost of the work that gets done, so the cost for a virtual function call is about the same as the cost for a normal function call.

For example, if a system or application spends 5% of its CPU utilization performing the linkage for function calls, and 25% of those calls are converted to virtual function calls, the additional overhead will be 10% of 25% of 5%, or around one-tenth of one percent overall.

If you can afford a normal function call, you can almost always afford a virtual function call.