I'm working on research that should be sent to publishing in the next couple of weeks. The research is done by me and a friend of mine; we are both under the same professor. This started as an attempt to improve on another paper which I'm the third writer on, but it quickly turned into a new idea which we will try to publish as a separate paper; because of this weird sequence of events, we didn't talk about who takes the lead. I'm taking tasks on almost every field of the research (building taxonomy, writing code, running experiments, writing the paper itself, etc.). I'm also considering the amount of ideas and implementations that wouldn't be done if not for me. I would say that overall my contribution is around 40%.
In my field, it's common to have an "equal contribution" footnote if two or more authors contributed equally. What is the common standard to ask for an "equal contribution" footnote?