I always thought Oh and my arrangement was pretty normal - we calculate our shared costs (mortgage, bills, food etc) and split them in two. We then both put that about plus about 5% or so into a joint account. The rest of our money is for ourselves and treat each other as we see fit.
But after some previous advice here and from reading other threads it seems this method is largely viewed as selfish or weird...
We don't have children but I imagine when we do we'll just roughly calculate the extra costs and split them too.
How do other people manage theirs?