How much will the SEO site drop after changing the domain?

Question

Search Engine Optimization

Hello, for some reason, I need to change the domain name of the site, while I do not lose the old domain and I plan to redirect from each page I visit.
Question - How likely is the fall of the site on SEO? Now stay in the top 1-3 for key queries

Answer 1

Make a redirect to a new domain, I think it will drop by 70%, then it will catch up.

Answer 2

strange question, to zero,
but after reindexing, how will it go