Shared ownership calculator, 2026/27

How this is calculated

Shared ownership splits the cost of a home between a mortgage on the percentage share you buy, typically 10% to 75% of the property's value, and rent paid to the housing association on the remaining share they retain. This calculator estimates the interest cost on your mortgaged share and the rent on the unowned share separately, then adds them together for a monthly total.

Rent on the unowned share is usually set as a percentage of its value, commonly around 2.75%, though this varies by scheme and by provider, and typically rises each year. Because the rent is set on the unowned value rather than the full property, buying a larger share reduces rent but increases the mortgage commitment.

Stamp Duty Land Tax on shared ownership purchases works differently to a normal purchase. Buyers can elect to pay SDLT on the full market value of the property at outset, which then means no further SDLT is due until their share reaches 80% or more, or pay SDLT only on the share initially bought, with further SDLT potentially due as the share increases through staircasing.

Staircasing and the SDLT election

Staircasing is the process of buying further shares in the property over time, eventually reaching full ownership in many schemes. Each staircasing transaction can attract further SDLT if the buyer did not make the upfront market-value election, calculated against the residential bands on the incremental value bought.

Choosing the upfront election makes sense for buyers confident they will staircase significantly over time, since it avoids repeated SDLT calculations and filings, while paying SDLT only on the initial share suits buyers unsure whether they will ever buy more than their starting share.

Other costs to budget for

Alongside mortgage and rent, most shared ownership leases include a service charge covering buildings insurance, communal repairs and management fees, which is payable regardless of the share owned and should be added to the monthly cost figure for a realistic budget.

Buyers should also check whether the lease requires the full 100% of buildings insurance to be arranged even on a part-owned property, and factor in the usual costs of buying, including legal fees, valuation fees and a mortgage arrangement fee.

How is rent calculated on the unowned share?

The housing association typically charges an annual rent, often around 2.75% of the value of the share they still own, though this varies by scheme, paid monthly alongside your mortgage and usually increasing each year.

Do I pay Stamp Duty Land Tax on a shared ownership purchase?

You can choose to pay SDLT on the full market value upfront, avoiding further SDLT until you own 80% or more, or pay SDLT only on the initial share bought, with more potentially due as you staircase to a larger share.

What is staircasing?

Staircasing is buying additional shares in your shared ownership home over time, gradually increasing your ownership percentage and reducing the rent payable on the remaining, smaller, unowned share.

Is shared ownership cheaper than buying outright?

It can reduce the deposit and mortgage needed initially, but the combination of mortgage interest, rent and service charge should be compared carefully against the cost of a smaller outright purchase or continuing to rent.