UK Shared Ownership monthly cost.
Total monthly cost
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Mortgage on owned share
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Rent on unowned share
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Your breakdown
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Part buy, part rent, and how the cost splits
Shared ownership lets you buy a share of a home, usually between 25% and 75%, with a mortgage, and pay rent to a housing association on the part you do not own. This calculator adds the two together. It works out the repayment mortgage on your owned share from the price, your deposit-adjusted rate and term, then adds the monthly rent, which is typically charged at around 2.75% a year of the value of the unowned share. The result is the true monthly outgoing, which is the number that actually decides whether the home is affordable.
A 35% share of a £300,000 home
Run the defaults: a £300,000 property, a 35% share, a 5% mortgage rate over 30 years, and rent at 2.75%. You own £105,000 of bricks and owe rent on the other £195,000. The repayment mortgage on £105,000 at 5% over 30 years is about £564 a month. Rent on the £195,000 unowned share at 2.75% is £5,362.50 a year, or £446.88 a month. Combined, the home costs £1,010.54 a month before service charges, ground rent or buildings insurance.
The two bars are close in height, which surprises first-time buyers. Almost half your monthly cost is rent on property you will never own unless you staircase. That is the central trade-off of the scheme: a smaller deposit and a lower mortgage, in exchange for paying rent that builds you no equity.
The costs this figure leaves out
The monthly total above is mortgage plus rent only. Real shared-ownership budgets carry more. You pay a monthly service charge, often £100 to £250 on a flat, plus buildings insurance and any ground rent. Crucially, on most older leases you are responsible for 100% of repairs and maintenance even though you own only 35% of the home. Newer leases under the 2021 model offer a 10-year window where the landlord covers some essential repairs, but check which version you are signing. Add these to the £1,010.54 to get a realistic total.
Staircasing, and the rent that keeps climbing
Buying more of your home is called staircasing. Each step needs a fresh valuation paid for by you, plus legal and mortgage fees, and SDLT can apply once your total share passes certain points. Two things make the maths move over time. First, your rent is usually reviewed annually and rises with inflation, often RPI plus a margin, so the rent figure in this tool will not stay still. Second, as house prices rise, each new share costs more, so staircasing early is generally cheaper than waiting. If you can foresee staircasing to 100%, model it as a goal, because reaching full ownership removes the rent line entirely.
Can I sell a shared-ownership home whenever I want?
Usually not freely. Most leases give the housing association a nomination period, often eight weeks, during which they can find a buyer before you market it openly. You sell your share at its current valuation, so you keep any growth on the part you own, but the process is slower than a standard sale.
Does the rent count toward my mortgage affordability?
Yes. Lenders treat the rent as a committed monthly outgoing when they assess how much they will lend on the owned share. A higher rent reduces your borrowing capacity, which is why some buyers choose a slightly smaller share to keep the combined cost within a lender's limits. It is a genuine trade-off worth modelling here: a larger share means a bigger mortgage but less rent, while a smaller share flips that around. Run two or three share percentages through the calculator and watch how the total monthly cost barely moves, because what you save in rent you tend to pay back in mortgage. The right share is usually the largest one your deposit and your lender will comfortably support, since rent buys you nothing you keep.