How shared ownership mortgages work
Quick answer: A shared ownership mortgage borrows against a share of a home — typically 10% to 75% — while you pay rent on the part you don't own. Two separate assessments decide whether you can go ahead: the housing association's own affordability model, and a lender's. They measure different things, which is why a straightforward-looking case can still stall, and why the lender you end up with depends as much on the share you're buying as on your income. This guide covers how the mechanics work, without naming specific lenders or products, since which ones fit — and what they'll lend — genuinely varies and changes over time.
How buying a share works
Shared ownership lets you buy a percentage of a home — usually from a housing association — and take out a mortgage against just that share. You pay rent on the remaining percentage, plus a service charge if the property is a flat or on an estate with shared facilities.
A home valued at £250,000 with a 40% share bought means a purchase price of £100,000 for the share itself. Your mortgage and deposit are worked out against that £100,000, not the full £250,000 — the key difference from a standard purchase.
Shares typically start around 10% and go up to 75%. The share you choose changes your rent, your deposit, and which lenders will consider the case.
The two affordability checks
Every shared ownership purchase has to clear two hurdles that measure different things.
The housing association's assessment comes first, often called the Homes England affordability assessment (the model most English housing associations use, adapted regionally elsewhere). It looks at your income, outgoings, deposit and the rent on the unsold share, and produces a recommended share size, typically capping what proportion of your net income can go on housing costs — rent plus mortgage combined.
The lender's own check comes second, once you have a share size in mind, and works like a standard mortgage assessment, but with the rent on the unsold share counted as an outgoing.
The two checks don't always agree — passing one and coming out tight on the other is common, and neither is wrong. Pairing the share size a housing association will approve with the mortgage a lender will actually offer against it is most of the job.
Your deposit is on the share
Because the mortgage is against the share, the deposit is too. A 5% or 10% deposit on a 40% share of a £250,000 home means 5% or 10% of £100,000 — a smaller cash requirement than 5% of the full price, one reason shared ownership appeals to buyers who can't yet stretch to a full-price deposit.
Not every lender treats a small deposit the same way, though: some set a higher minimum specifically for shared ownership, and new build versus existing, house versus flat, and location can all move that minimum.
Rent and service charge count against you
The rent on the unsold share — and, on a flat or shared estate, the service charge — is counted by the lender as a committed monthly outgoing, the same as any other regular payment.
That reduces how much a lender will offer compared with a standard purchase, where there's no equivalent outgoing. It's also why the share size is a genuine trade-off: a bigger share means more mortgage and less rent; a smaller share means less mortgage but more rent eating into what a lender will lend.
Why lenders differ on the share
Not every UK lender offers shared ownership mortgages, and among those that do, the details differ. Some cap the share they'll lend against — commonly 85% to 100% — beyond which you'd need to staircase first. Some lend on flats but not houses, or the reverse. Some restrict lending to new build only, or exclude it. A handful of lenders and schemes are England-only.
We don't publish lender names here, because which ones fit changes with your share, deposit, property type and location — and because criteria move. What matters is that the field is narrower than for a standard mortgage, and picking the wrong lender first can cost weeks against a reservation deadline a housing association won't always extend.
Staircasing
Staircasing is buying a bigger share after your initial purchase — say, 40% to 60%, or eventually 100% — with the housing association revaluing the property each time. It's worth thinking about before you complete: a lender that caps its lending at 75% of the share won't take you to 100% later without a further application, and some lenders make staircasing to full ownership more straightforward than others.
What an adviser does
A shared ownership case involves two assessments, not one, so an adviser does two jobs in parallel: presenting your figures so the housing association's affordability model reads them clearly, and matching your share, deposit and property type against the narrower panel of lenders who actually offer shared ownership.
A tight or negative result from the housing association's own calculator is often not the end of the road — it's frequently about how the figures were entered, or a share size that needs adjusting, and an adviser can talk that through with the housing association directly. A decline from one lender rarely means a decline everywhere.
You can get an indicative lender answer first with the free shared ownership mortgage calculator — enter the full price, the share, your deposit, the rent and the service charge, and see what a lender's own affordability check would make of those numbers before you talk to anyone.
FAQ
Can I get a shared ownership mortgage with a small deposit?
Often, yes — the deposit is measured against the share, not the full property value, so 5% or 10% of the share is a realistic starting point. Which lenders accept that depends on the property type and location.
Do I have to use the lender the housing association recommends?
No. Housing associations don't require a specific lender — they need to see that your assessment and mortgage offer support the share you're buying.
What happens if I can't afford the share I wanted?
The housing association's assessment will usually recommend a smaller share, and most schemes let you start smaller and staircase up later.
Is shared ownership only for first-time buyers?
No. Many schemes also accept people who've owned before but can no longer afford the open market — eligibility varies by scheme and area.
Capital Mortgage Advice opens its full advice service in September 2026 — until then, this guide is for information only, not a recommendation about any specific lender, product or course of action regarding a shared ownership purchase. Join the launch list to hear when advice goes live.
General patterns around shared ownership reflect Homes England's published guidance and standard UK lending practice, checked September 2026 — no figures or thresholds here are specific to any single lender or housing association, and actual acceptance criteria vary and change over time. This guide is information, not financial advice.