Proportional bills split (UK): a calm, repeatable method
Couples often argue about “fair” because bills don’t care who earns more. A proportional split makes the rule explicit: you each contribute in line with take‑home pay, then you both keep a reasonable leftover.
Decide what counts as “shared”
Start by agreeing what you’re splitting. In most UK households that means mortgage (or rent), council tax, utilities, home insurance, and a maintenance buffer. Groceries are the big judgement call: some couples split groceries as shared costs, others keep them separate.
The calculator supports both approaches. If groceries feel contentious, try it both ways and compare the leftovers.
Make it feel fair (not just “correct”)
A proportional split can be mathematically tidy and still feel emotionally wrong if one person feels they’re “subsidising” lifestyle choices. The practical fix is to agree a shared baseline (the home and essentials), then keep discretionary spending personal.
If you’re stuck between methods, compare proportional vs a simple custom split like 66/33 vs 50/50 and choose the one that keeps both leftovers sustainable.
Proportional split formula (plain English)
Add your take‑home pay together. Your share is your take‑home divided by the total. Multiply the shared monthly total by that share. That’s what you pay.
The key output is the leftover: take‑home minus your share. If one person’s leftover is consistently squeezed, you’ll feel it in the day‑to‑day.
Where proportional can break down
- One person paid most of the deposit and you want to “rebalance” in monthly payments.
- Income is volatile (commission / self‑employed) and you want a simpler rule.
- You prefer a fixed custom split (like 66/33) for emotional simplicity.
Worked examples
Each example shows (1) the shared monthly total, (2) proportional vs 50/50, and (3) leftovers.