
For rent, the simplest fair method is to price the rooms, not the people. Agree on a premium for the large room with the private bath (realistically $150–$300 depending on size and bath value), then split the remainder equally. Example: if rent is $3,000 and you set a $200 premium, the big room pays $1,200 and the other two pay $900 each. If you also want to reflect income, only apply income weighting to the common-area portion: subtract room premiums first, then split what's left by each person's percentage of total household income so the room value and income both get acknowledged without overcomplicating it.
For tracking and preventing constant pay requests, set up a Splitwise (or Settle Up) group for the apartment. Add recurring monthly expenses for Rent, Electric, Gas, Internet; set Rent to split "unequally" with the premium, and split utilities evenly unless someone has clearly higher usage. One person autopays the landlord and utilities, and all three of you set a scheduled bank transfer or Zelle on the 27th for whatever Splitwise shows so you settle once per month with one payment; build in a 2–3 day buffer and agree that any late fees get covered by the late payer.
For shared items, avoid nickel-and-diming by either funding a small house kitty ($20–$30 each per month tracked in Splitwise) or rotating the monthly buyer with a soft cap (around $40). Use the kitty only for staples like paper goods, soap, trash bags, and spices; label personal food, and only split groceries when you all agree it's a shared meal or the shared portion is over a simple threshold like $10. Keep a whiteboard or note for the shared list so whoever shops buys from it, then log it once, not receipt-by-receipt.