Split all household expenses proportional to income. It's easy to do, and really stable over time. Works for things like shared housing situations too. If you

Split all household expenses proportional to income. It's easy to do, and really stable over time. Works for things like shared housing situations too. If you want to be even fairer, take $50,000 off the bottom, and then split all expenses for non-survival stuff proportionately to income over $50,000.