Do you split expenses 50/50 with your partner, even when you don't earn the same?

My partner and I earn very different amounts, and my income is irregular on top of that. For years we did the easy thing: everything 50/50. Fair on paper, less fair in practice, because the same 600 EUR of rent isn't the same effort for both of us.

Curious how other couples and roommates handle it:

Straight 50/50

Proportional to income

One covers the fixed costs, the other the variable ones

Fully separate, nobody counts

I'm especially interested in the edge cases: what happens when one of you is between jobs, or when someone earns 3x the other? Has your split rule ever caused an actual argument?

Full disclosure: I'm building Splinity, launching here on September 8, a budget app where you define the split rule yourself. But I'd have asked this question anyway.