What is a reasonable equity split where two people have been working separately on a similar tech idea and are now looking to join forces. These individuals are friends. Despite both working tirelessly on their respective apps, and investing heavily, one has made more progress on the app and has achieved a fit for purpose ready to launch early version. She is inviting the other to join her for an equity stake in the combined business. The friend brings distinct skills and will be pivotal in developing a second market for the app (which is where she has been focussing her efforts). Both share a similar vision for the product, and passion.
The venture is pre-revenue (it hasn't officially been launched yet, and there are no customers), and pre-investment.
Is it reasonable to offer a 80/20 split?
Or is it fairer to offer higher for the person being invited?
When talking founders, the best default starting point is an equal split of equity (50/50 in your case). While I think your situation merits considering something besides 50/50, there are two items that I think ought to still push it back to 50/50, or at least closer than 80/20.
The first thing is, it sounds like the new person is a non-technical person and the technical side is effectively complete. Which means that the non-technical person still has their work cut out for them. They'll still be doing enough work -- likely enough to justify 50% of the equity.
The second point that I want to mention is that you can still split equity at 50/50, and have each person's shares vest differently. Founders often have their equity vest over a period of four years (or something like that) with a one year cliff (they get nothing until they complete their first full year). If founder #1 has been working on the project for a year already, they could just start 1 year into the vesting process, while founder #2 is starting at the beginning. In four years when both founders are fully vested, the fact that you started at different times will mean practically nothing.
50/50 may not be the only option, but 80/20 seems like a bad deal for founder #2 to me.