Dreamcraft, a Danish VC fund, has conducted an analysis on the dilution of founders in tech startups. The material finding is that the median dilution goes from 18.6% in pre-seed rounds, to 20.3% in seed rounds, 23.5% in series A, and 14.7% in series B+, meaning that founders should have it as a rule of thumb to be diluted 20% per round in early stages.
See the full overview here.
