In many places, you don't. Washington State all property is 50/50. Half my income is my wife's, even though I make 800k and she makes nothing.
I dunno, the idea that you are willing to make a commitment to someone for the rest of your life but also try to hold back money from them is so alien.
My rationale is that prenups are an acknowledgment that sometimes, people discover things don’t work out. Agreeing what each person has from the beginning confirms the commitment of marriage is beyond the money/wealth that existed before.
I’ve never been married yet but this perspective seems rare. So many people’s lives get destroyed or seriously damaged after a bad divorce. Why not do something that would ease the pain for both parties?
The alternative is to say, "knowing who we are now, we are going in together. Fifty fifty. Egalitarian. If someday in the future we split, we both walk away with half."
Holding on to the idea that somehow anything is "mine" or "yours" rather than "ours" is a waste, imo. You can try and protect "mine" with a prenup, or you can accept the "ours" nature and make peace with that. I find the latter to be simpler, more elegant.
Even though Washington is a community property state, you can still have a prenup agreeing that your two incomes will be separate property, if you so wish and if you execute it correctly.
I dunno, the idea that you are willing to make a commitment to someone for the rest of your life but also try to hold back money from them is so alien.