Shared Ownership Calculator

Shared ownership lets you buy a share of a property, between 25% and 75%, and pay rent on the remaining share, which stays with a housing association. You need a mortgage only for the part you are buying, plus a deposit on that share alone, typically 5-10% of its value. On a £300,000 property that is the difference between finding a deposit against the whole £300,000 and finding one against the £150,000 half you are actually purchasing, which is why the upfront cost falls so sharply compared with buying outright.

Monthly costs come in four parts: the mortgage on your share, rent to the housing association on the share you do not own, service charges and any ground rent. The rent is typically 2.75% of the unsold equity a year, so on that £300,000 property with a 50% share, the rent on the other £150,000 works out at £344 a month. A mortgage of £150k at 5% over 25 years adds £877, giving £1,221 a month in total against £1,754 for buying the whole property. The trade is plain enough: a lower monthly cost now, but only 50% of any capital appreciation later.

Rent on the unsold share usually rises each year by CPI plus 1%, although newer leases may cap increases at CPI alone. Over a long tenure that clause matters more than the headline rate, because the rent climbs whether or not your mortgage does. This calculator breaks down all the monthly costs of a shared ownership purchase. Enter the property value, the share you are buying, your deposit and the interest rate, and it sets the result against renting or against buying the whole property with a larger mortgage.

Buying more of your home is called staircasing, and it usually becomes available after a year of living there. Transactions have historically had a minimum size of 10%, but the 1% staircasing model introduced in 2021 allows annual purchases of 1% at fixed RPI-linked valuations. Most properties can be staircased all the way to 100%, the exception being designated protected areas, generally rural or coastal, where the cap is 80%. Each step carries its own SDLT, legal fees and valuation costs, and because the valuation follows the market, a rising market makes every additional percentage dearer than the last.

Eligibility is means-tested and capped. For 2026/27 household income must be under £80,000, or £90,000 in London, and you must be unable to afford a comparable home outright. Beyond that you need to be a first-time buyer, an existing shared owner staircasing, or a home mover who cannot afford a full purchase. Some schemes prioritise applicants with a local connection or key worker status. You apply to the organisation selling the home, usually a housing association or council, which checks eligibility and affordability, and because supply is limited, properties are often allocated within weeks of release.

The risks are real and worth reading in full before committing. On older leases you are 100% responsible for repairs and maintenance, including on the share you do not own; homes sold under the 2021 model come with a 10-year initial repair period in which the landlord covers major repairs and up to £500 a year of essential ones. Service charges on new builds can run to £200-£500 a month. Resale is restricted, because the housing association usually has first call on finding a buyer. The lender market is narrow, with fewer products and often higher rates than mainstream mortgages. The structure is leasehold, which brings ground rent and exposure to future reform. None of that rules shared ownership out, but the lease is the document that decides how each of these points plays out in your case.