Shared Ownership Calculator UK
Work out the mortgage, rent and service charge on a shared ownership home, what it costs to staircase to a bigger share, and which stamp duty option is cheaper.
Last updated: October 2026 · 2026/27 stamp duty rates
The home and your share
Between 10% and 75%, usually at least 25%.
Usually 5% to 10% of the share you buy.
Monthly costs
Assumption: 2.75% of the unsold share's value a year is a typical figure, not a rule. Use the rent in your lease or key information document.
Staircasing
Further shares are priced at the market value at the time, so they cost more if prices rise.
Total monthly cost
£1,112.80
Mortgage £600.30 + rent £412.50 + service charge £100.00
Your purchase
| Share price (40% of £300,000) | £120,000 |
| Deposit | £12,000 |
| Mortgage | £108,000 |
| Monthly mortgage payment | £600.30 |
| Unsold share value | £180,000 |
| Monthly rent (2.75% a year × £180,000 ÷ 12) | £412.50 |
| Service charge | £100.00 |
| Total monthly cost | £1,112.80 |
Stamp duty options (England and Northern Ireland)
Pay in stages, on the share
£0
On £120,000 now. More may be due once your share goes over 80%.
Market value election
£0
On the full £300,000 now. Nothing more to pay when you staircase.
First-time buyer relief applied: the full market value is within £500,000. In Scotland and Wales, LBTT and LTT apply instead.
Staircasing to 50%
| Extra share bought | 10% |
| Cost at £300,000 market value | £30,000 |
| Monthly rent afterwards | £343.75 |
Assumes rent falls in proportion to the share you still rent. Valuation and legal fees for staircasing are extra.
How it works
With shared ownership you buy a share of a home, between 10% and 75% of its full market value (usually at least 25%), take out a mortgage on that share, and pay rent to the landlord, usually a housing association, on the part you do not own.
Worked example. A £300,000 home, buying a 40% share. The share costs £120,000. A 10% deposit is £12,000, so the mortgage is £108,000, which at 4.5% over 25 years costs £600.30 a month. The landlord still owns £180,000; at an assumed rent of 2.75% a year that is £180,000 × 2.75% ÷ 12 = £412.50 a month. Before any service charge, the total is £1,012.80 a month.
The mortgage uses the standard capital-and-interest formula with interest charged monthly, as in our mortgage calculator. Because you only borrow against your share, the deposit and income needed are far lower than for buying outright, but lenders count the rent and service charge as commitments when they assess what you can afford. Compare with buying outright using the mortgage affordability calculator.
In England and Northern Ireland you choose between two ways to pay Stamp Duty Land Tax:
- Pay in stages. SDLT is worked out on the price of the share you buy now. You pay nothing more, and do not file a return, when you staircase until your share goes over 80%. At that point SDLT is due, with all your share purchases treated as linked.
- Market value election. You pay once, on the full market value stated in the lease, and never pay SDLT again on later shares. The election cannot be cancelled.
First-time buyer relief can be claimed on either route, but only if the full market value of the home is £500,000 or less. On the £300,000 example a first-time buyer pays £0 either way, and staircasing later does not withdraw the relief. Someone who is not a first-time buyer pays £0 in stages now or £5,000 with an election.
Above the cap there is no relief at all. On a £600,000 home with a 50% share, paying in stages costs £5,000 now, against £20,000 for an election. Paying in stages is cheaper today, but if you expect to staircase beyond 80% when prices are higher, an election can work out cheaper. See our stamp duty calculator and guide to how stamp duty works.
This calculator leaves out SDLT on the rent element of the lease, which HMRC only charges where the rent is large; first-time buyers claiming relief pay none on it.
Affordability calculators
This calculator is part of a family. The main calculator covers the general case.
Main calculator: Mortgage Affordability Calculator
How much UK lenders will typically offer at 4.5×, 5× or 5.5× income with your deposit.
Related calculators
Other free UK tools that follow on from this calculation.
Mortgage Affordability Calculator
How much UK lenders will typically offer at 4.5×, 5× or 5.5× income with your deposit.
First-Time Buyer Stamp Duty Calculator
First-time buyer SDLT in England and NI, with the eligibility check and the cliff edge just over £500,000.
Lifetime ISA Calculator
Project savings with the 25% government bonus for a first home or retirement.
Mortgage Calculator
Monthly repayments, total interest and LTV for any UK mortgage scenario.
Reviewed by Alexandre Bernier, LLM (UK), CFP®
Educational tool: estimates only. Not individual financial, investment, tax or legal advice. Using it does not create an adviser-client relationship. Rules and figures change; check them against current HMRC and GOV.UK guidance and speak to a qualified professional. Editorial policy →
Sources
Every rate and threshold used by this calculator is taken from the official pages below. If a figure here disagrees with one of these, the official page is right, please tell us.