Partner moves in later: how to split costs fairly
When one person already owns the home and the other moves in later, couples often get stuck between “fair contribution” and “ownership”. A calm approach separates the two: agree a monthly shared-cost system that both can afford, and treat ownership/legal structure as a separate conversation.
Use the calculator to agree a monthly contribution
Opens the main calculator prefilled so you can define shared costs and compare proportional vs custom splits with real numbers.
No signup. Private. Links are shareable and can be reset anytime.
A practical framework that stays low-friction
- Define shared costs (housing + core bills + maintenance buffer; groceries optional).
- Choose a split rule (often proportional, sometimes a fixed custom split for simplicity).
- Check leftovers and stress tests (+1%, +2%, one-income) to make sure it’s resilient.
- Keep ownership/tenancy/legal arrangements separate (and get proper advice if you need it).
This is budgeting guidance only — not legal advice. The goal is a sustainable monthly plan you both feel good about.
Worked examples (with numbers)
Example 1: proportional shared costs once living together
Total shared cost: £2,602 / month
Proportional: A £1,561 · B £1,041 · 50/50: A £1,301 · B £1,301
Selected mode: proportional · Leftovers: A £2,039 / B £1,359
Example 2: custom split for a stable agreement
Total shared cost: £2,978 / month
Proportional: A £1,985 · B £993 · 50/50: A £1,489 · B £1,489
Selected mode: custom · Leftovers: A £2,115 / B £1,207
FAQ
Should the person who already owns the home pay everything?
Not necessarily. Many couples treat the mortgage as a housing cost and agree a contribution that’s fair and sustainable. The key is clarity about what the payment represents (budgeting vs ownership).
Is this advice about rent or legal ownership?
No. This is budgeting guidance about monthly affordability and fairness. Ownership, tenancy, and legal arrangements are separate topics.
What’s the simplest system?
Define a shared-cost list, pick a split (often proportional), and review after a set period. Keep personal spending personal to avoid micromanagement.
How do we avoid awkwardness?
Write down the rule you agreed and what it covers. The goal is to avoid “monthly negotiation” and keep the system calm and predictable.
Explore related UK guides
Quick links: split bills living together, partner earns more — what’s fair?, buy in one name or joint.
Related guides
How to split bills when living together
A clear 3-step system that avoids monthly negotiation.
What counts as shared costs?
A clear shared-cost list and what to keep personal.
Should groceries be shared 50/50?
50/50 vs proportional vs hybrid grocery splitting.
Mortgage & bills split calculator
Run your numbers live and share a scenario link.
How the maths works
Mortgage formula, totals, leftovers, and what’s included.
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).
60/40 bills split guide
A simple compromise between 50/50 and proportional.
Tip: open a guide in one tab and the calculator in another to compare options quickly.