How to choose a custom split (60/40 or 66/33) without guesswork
Custom splits can be emotionally easier than proportional rules. This page shows a practical way to pick a custom split: start with a goal (balanced leftovers), then validate it with rate‑rise and one‑income stress tests.
Prefer to start from the hub? Open the main calculator.
Calculator
Worked examples
Each example uses the same calculator engine. Use “Open in calculator” to share or compare scenarios.
Start at proportional, then lock in a custom split
Incomes: A £4,200 · B £2,600
Shared total: £3,361 / month
Split (proportional): A £2,076 · B £1,285 · Leftovers: A £2,124 · B £1,315
Lock to 66/34 and compare the leftovers
Incomes: A £4,200 · B £2,600
Shared total: £3,361 / month
Split (custom): A £2,219 · B £1,143 · Leftovers: A £1,981 · B £1,457
FAQ
Is choosing 66/33 “unfair” to the higher earner?
Not necessarily. It can be fair if both people agree on the trade‑off and the plan is sustainable. The best test is whether both people keep a healthy leftover and you can still save.
Should we adjust the split for a bigger deposit?
Some couples do, especially if one person contributed significantly more upfront. Use a custom split and see how it changes leftovers over time; consider documenting your agreement.
How often should we revisit a custom split?
At milestones: job changes, parental leave, rate refixes, or major cost changes. A stable rule can be good, but ignoring reality can create resentment.
Related links
Related guides
Mortgage & bills split calculator
Run your numbers live and share a scenario link.
50/50 vs proportional vs custom splits
Choose a split that feels fair and stays sustainable.
Split the mortgage by income (UK)
Proportional splits explained with worked examples.
Proportional bills split calculator guide
Turn take-home pay into a clean monthly split.
66/33 vs 50/50 split for couples
When a custom split beats proportional (and when it doesn’t).
Stamp Duty (SDLT) calculator for couples
Standard vs first-time buyer relief + surcharges.
60/40 bills split guide
A simple compromise between 50/50 and proportional.
70/30 bills split guide
When a fixed split makes sense (and how to validate it).
75/25 bills split guide
For very different incomes: keep leftovers and resilience in view.
Should we split the mortgage 50/50?
A simple decision framework using leftovers and stress tests.
Tip: open a guide in one tab and the calculator in another to compare options quickly.