How to calculate Execution time overhead

A Coworker and I do not seem to be on the same page regarding how to correctly calculate overhead.

Example:: Implementation A takes 30 min for a workload, and Implementation B with additional Overhead due to software design takes 50 minutes.

What is the most applicable Method to calculate the overhead?

Opinion 1 : 50/30 = 160% so ~60 % overhead

Opinion 2: 50 is close to 2*30 so closer to ~80% overhead.