About the UK Shared Ownership Calculator
Shared ownership lets you buy a share of a home — typically between 10% and 75% — with a mortgage and deposit, and pay rent to a housing association on the part you do not own. This calculator works out the cost of your share, the deposit and mortgage, the monthly rent and the all-in monthly cost including the service charge.
It also models staircasing: buying more shares later. Additional shares are priced at the home’s market value at the time you buy them, so the calculator projects the value forward at a growth rate you choose and shows the cost of the extra share and how much your rent falls afterwards.
Rent is commonly set at around 2.75% to 3% of the value of the unsold share per year, and leases usually let it rise each year; the calculator uses today’s figure. Check the provider’s key information document for the actual rent, service charge and minimum share, and remember that mortgage lenders lend only on the share you buy.
With the default inputs, the total monthly cost is £1,095.88. Change any value above to recalculate instantly.
How to use the uk shared ownership calculator
- 1Enter the full market value and the share you plan to buy.
- 2Set your deposit percentage, mortgage rate and term.
- 3Enter the rent percentage and service charge from the provider’s key information document.
- 4Choose an extra share to staircase, a growth rate and when you would buy it.
- 5Review the monthly cost and what staircasing would cost.
Formula and method
The share price is the full market value times the share you buy. Your deposit is a percentage of that share price and the mortgage covers the rest, repaid with the standard formula M = P × r(1 + r)^n ÷ ((1 + r)^n − 1). Rent is charged on the share you do not own at the annual rent percentage, divided by 12.
For staircasing, the home value is grown at g per year for t years and the extra share is priced at that future value, as providers use a fresh RICS valuation. Rent after staircasing falls in proportion to the remaining unowned share. Annual rent increases, staircasing fees and the cost of a new valuation are not included.
- Value
- Full market value of the home
- share
- Percentage of the home you buy
- rent%
- Annual rent as a percentage of the unowned share
- g, t
- Annual house price growth and years until staircasing
Worked examples
40% share of a £300k home
A 40% share costs £120,000; a 10% deposit leaves a £108,000 mortgage at £563 a month. Rent of 2.75% on the £180,000 you do not own is £412.50 a month, and with a £120 service charge the total is about £1,096. Buying another 10% in 5 years, with 3% growth, would cost about £34,778 and cut rent to £343.75.
25% share with 5% deposit, staircasing to 50%
A 25% share is £62,500 and a 5% deposit of £3,125 leaves a £59,375 mortgage at £347 a month. Rent at 3% on £187,500 is £468.75. With flat prices, buying another 25% costs £62,500 and reduces rent to £312.50 a month.
50% share of a £400k flat, staircasing 40% in 10 years
A £200,000 half share with a 5% deposit needs a £190,000 mortgage at about £963 a month. Rent on the other £200,000 is £458 and the service charge £150, so the total is £1,571. After 2% annual growth the home is worth about £487,600 in 10 years, so a further 40% would cost about £195,039.
Frequently asked questions
How is shared ownership rent calculated?+
Rent is a percentage of the value of the share you do not own, commonly around 2.75% to 3% a year at the start, divided into monthly payments. It normally increases every year by a formula set out in your lease, often linked to inflation.
What is staircasing?+
Staircasing means buying additional shares in your home. Each extra share is priced at the current market value, based on a RICS valuation, so if prices have risen you pay more than you would have at the start. Your rent falls as your share rises, and at 100% it stops.
How much deposit do I need for shared ownership?+
Deposits are based on the share price, not the full value. Many lenders accept 5% of the share — for a 25% share of a £250,000 home that is £3,125. A larger deposit can secure a better mortgage rate.
Do I pay service charges on shared ownership?+
Yes. You usually pay the full service charge and buildings insurance contribution for the property even though you own only part of it. Some newer leases include help from the landlord with certain repair costs in the early years, so check your lease.
Who is eligible for shared ownership?+
In England you generally need household income of £80,000 or less (£90,000 in London) and must be a first-time buyer, a former owner who cannot afford to buy now, forming a new household, or an existing shared owner moving home. You must also show you cannot afford a suitable home outright.
Results are estimates for educational purposes and are not financial advice. Rates, fees and terms vary — confirm with your lender or a licensed advisor before making decisions.