Half Buy Half Rent Calculator

“Half buy, half rent” means three different things, and this calculator handles all three in separate tabs. In the UK it is shared ownership: you buy a share of a home, mortgage that share, and pay rent on the share you do not own. For everyone else it is either the rent vs buy breakeven question, answered with the renter fairly credited for investing the difference, or the house hack: buy a property, live in part of it, and rent out the rest so a tenant covers part of your housing cost.

Quick Answer

How to use this half buy half rent calculator

Pick the tab that matches your situation, check the pre-filled example, then swap in your own numbers and click Calculate. Results stay hidden until you do. The three tabs share no inputs, so changing one tab never disturbs another.

This page is not the same as a standard rent-or-buy tool. A generic rent vs buy calculator answers one question about one whole home. This page exists for the part-ownership cases that question misses: the shared ownership buyer who owns half a home and rents the other half, and the house hacker who owns all of a property but rents part of it out. The middle tab covers the classic question too, but with the renter's invested down payment counted honestly, which is where most simple tools quietly tilt the answer toward buying.

Two input habits apply across tabs. The shared ownership and rent vs buy fields accept commas (300,000 works), because they read whole numbers as typed. The house-hack fields do not strip commas, so type plain numbers there. And on every tab, the mortgage itself is an ordinary repayment mortgage: if you want to isolate that payment from everything else, the mortgage payment calculator breaks a loan down on its own.

How each of the three models works

Each tab is a separate model with its own formulas. Nothing is shared between them except the standard repayment-mortgage payment, which all three compute the same way.

The shared ownership model is the arithmetic in the GOV.UK guide to shared ownership homes: your deposit and mortgage attach to your share only, while rent attaches to the landlord's share. The rent rate is not invented by this page: housing associations set it in the lease, initial rent is capped at 3% of the unowned share under the Homes England funding rules, and around 2.75% is the common starting figure, which is why the tab pre-fills it and lets you change it.

The rent vs buy model runs month by month, not year by year. Each month it charges the buyer the same fixed ownership cost (principal and interest, tax and insurance, maintenance), steps the rent up once every 12 months, grows the home's value smoothly, and moves the gap between the buyer's cost and the rent into or out of the renter's investment pot. Breakeven is tested only at each year end, on the two positions the table prints. One honest consequence: if rent is higher than the buyer's monthly cost, the renter's pot is drawn down each month, because the model assumes the renter invests the difference and there is no difference to invest. If you are modelling how today's rent grows into a future tenancy instead, the future rent calculator projects a rent figure on its own.

The house-hack model is deliberately narrower. It holds the collected rent flat, trims it by the vacancy allowance, adds a maintenance reserve calculated on that rent, and compares your net cost with the rent you would otherwise pay. No appreciation is counted anywhere in the tab, a point the verdict restates. Lenders treat this income more cautiously than the model does: under the Fannie Mae selling guide's rental income rules, only part of expected rent from a subject property counts toward qualifying, so a hack that works on this page still has to survive a lender's haircut.

Worked examples, one per tab

All three tabs are pre-filled with the examples below. Every figure quoted here was produced by running the calculator with exactly these inputs.

Shared ownership: a £300,000 flat at a 50% share

Buy 50% of a £300,000 flat (£150,000) with a £7,500 deposit, mortgage the remaining £142,500 at 5% over 25 years, pay 2.75% rent on the unowned £150,000 and a £120 monthly service charge. The tab returns a total of £1,296.79 a month. Halving the share to 25% cuts the mortgage far more than it cuts the total, because the rent on the unowned 75% climbs to £515.63:

Both runs include the same £120 service charge. The lesson in the table is the shape of shared ownership itself: a smaller share lowers your entry cost sharply (a £3,750 deposit gets you housed) but the rent line, not the mortgage line, becomes the bigger payment.

Rent vs buy: a $400,000 home against $1,800 rent

Buy a $400,000 home with 20% down at 6.5% over 30 years, $500 a month of tax and insurance, 1% yearly maintenance and 3% appreciation, against renting at $1,800 a month rising 3% a year with the spare cash invested at 7%, compared over 10 years. The buyer's monthly cost is $2,855.95, and there is no breakeven in the 10 years:

That surprises people, but it is the opportunity cost of the down payment doing its work: $80,000 compounding at 7% is a high bar for 3% appreciation to clear. Change the assumptions and the verdict flips hard: the same home at 5% appreciation with rent at $2,000 growing 2% and a 3% investment return breaks even in year 1, with a lower buyer cost of $2,451.16. Neither answer is the truth about your market; both are the arithmetic of the assumptions you typed, which is exactly why the tab prints them inside its verdict. A quick screen before running either model is the price-to-rent relationship, covered by the buy to rent ratio calculator for the investor side of the same question.

House hack: a $400,000 duplex with $1,200 of rent

Buy a $400,000 property with 20% down at 6.5% over 30 years, $500 a month of tax and insurance, collect $1,200 a month from the other unit, allow 8% vacancy and 5% maintenance on the rent, against an alternative rent of $1,800. The tab's verdict is Favorable:

Read the bars as the whole pitch of house hacking: the tenant's effective $1,104 does not cover the $2,582.62 cost of owning, and it does not need to. It only needs to pull your net cost ($1,478.62) below the $1,800 you would pay in rent, while the loan balance falls by $48,716.40 over the decade. Push the collected rent high enough and the same model turns Excellent: at $2,500 of rent on a $300,000 purchase in the tab, the net cost goes negative at $-661.63, which is the tool's way of saying the rent covers everything and pays you. Another common affordability screen for the renting side is the 40x rent rule calculator, which tests rent against income rather than against ownership.

Staircasing: buying more of your home later

Staircasing is buying extra shares after you move in, each priced at the home's market value at that time. Every extra share cuts the rent in direct proportion, and at 100% the rent ends, though the service charge usually continues.

The shared ownership tab illustrates one step on every run: on the £300,000 worked example, a further 10% costs about £30,000 at today's value and cuts the monthly rent by about £68.75, because 10% of the home stops being rented at 2.75% a year. Treat that line as an illustration at today's price, not a quote. As the GOV.UK staircasing guidance sets out, a real staircase is priced from a fresh valuation, newer leases (bought on or after 1 April 2021) may allow gradual 1% steps each year for the first 15 years, and standard steps are usually 5% or 10% or more, sometimes with an administration fee of roughly £150 to £500. If the home has risen in value, each step costs more than the illustration suggests, and your mortgage payment rises if you borrow to fund it while the rent falls.

What these models leave out, stated plainly

Each tab is a model, and each model leaves real costs out. Knowing which ones is the difference between using the output and being used by it.

• Shared ownership rent rises in real leases. The tab charges a flat rent rate for the whole term. Real shared ownership rents are reviewed yearly, typically upward with inflation under the lease formula, so a 25-year view at today's rent understates later years.
• Rent vs buy excludes transaction costs. The verdict says so itself: taxes (beyond the monthly tax and insurance you enter), closing costs and selling fees are not counted. Adding them pushes any breakeven later, so read an early breakeven as optimistic. The buyer's position also assumes you could sell at the appreciated value with no costs at the year you are measuring.
• The renter is assumed to actually invest. The rent vs buy renter invests the down payment and every month of difference, and withdraws from the pot in months where rent exceeds the buyer's cost. If the difference gets spent instead, the renter's line collapses and buying wins far earlier. The discipline is the assumption.
• House-hack principal is labelled "10 years" even on short loans. The figure totals principal over 10 years or the full term if shorter. On a 5-year loan it returns the entire loan amount ($160,000 on the test run) because the loan is fully repaid inside the window, and the verdict still frames it as equity built over 10 years.
• House-hack validation leaves a previous result on screen. In the house-hack tab, an invalid entry shows its error message but does not clear an earlier result, so read the error, not the numbers, until you have fixed the input and calculated again. The other two tabs hide their results on an error.
• No tax, benefits or eligibility logic anywhere. Shared ownership eligibility (household income caps of £80,000, or £90,000 in London), rental income tax on a house hack, and capital gains are all outside these models. This page is for education and planning, not financial or real estate advice.

What competing calculators miss

The three questions on this page are usually served by three separate tools, and each set of rivals has its own blind spot:

• UK shared ownership calculators (Santander, Legal & General Affordable Homes, broker tools such as AS Mortgages): solid on the core mortgage-plus-rent maths, and several explain the 2.75% rent convention well. But Legal & General's affordability tool excludes the service charge from its calculation by its own admission, most stop at the first purchase with no staircasing illustration, and none stress-tests the rent at a different rate the way changing one field here does.
• Shared ownership budget tools (Shared Ownership Budget Calculator): strong on true monthly cost and on the housing association's stricter affordability check, a genuinely useful angle. The gap is scope: no staircasing maths, no rent vs buy breakeven, no house-hack model, and the answer is a single monthly figure rather than a model you can interrogate.
• Rent vs buy calculators (PrimeCalculator, NeftCal, Lofty, CalculatorPark): the better ones now credit the renter with investing the difference, as this page does. Many still bury the assumptions, cap the horizon at 7 to 10 years without saying what changes beyond it, or report a single breakeven with no year-by-year table to audit. None of them touches part-ownership at all.
• House-hack calculators (VantoVault, WrenchAndWallet, FinExplained): richer investor metrics (cash-on-cash, cap rate, the after-you-move-out scenario) that this tab does not attempt. What they rarely do is the plain comparison this tab leads with: your net cost against the rent you would otherwise pay, with the equity built over 10 years stated in the same verdict.
• The gap this page fills: all three part-ownership questions in one place, each with its assumptions printed inside the result, service charge and staircasing included in the shared ownership model, and a rent vs buy engine that never hides the renter's invested down payment.

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