Work out net profit per property
"Am I making money?" is the wrong question. The right one is which property makes money — after the mortgage. Here's how to work out net profit for a single door, why the tax makes it trickier than it looks, and how to see it across a whole portfolio at a glance.
Plain English · UK landlords · not tax advice — check GOV.UK.
The cash view. The tax view differs — see below.
The one-door calculation
Net profit per property is a subtraction, done one property at a time. Take the rent that door actually brought in, take away what it cost to run, take away the mortgage — and you have the number that tells you whether the property earns its keep.
Rent received
The rent that actually landed for this property — not the rent on the tenancy agreement. Void months and part-payments count as they really happened.
Minus running costs
Everything it takes to keep the door let: letting and management fees, insurance, repairs, safety certificates, ground rent and service charges, accountancy — plus the cost of any voids.
Minus the mortgage
The mortgage payment on that property. For cash flow you subtract the whole payment; for tax it's treated differently — the catch we cover next.
Rent received − running costs − mortgage = net profit per property
Cash profit isn't taxable profit
For most individual landlords, the mortgage is where the simple sum gets complicated. Since April 2020, you can no longer deduct mortgage interest from rental income as an expense. Instead you get a basic-rate (20%) tax credit on the interest.
So there are really two numbers. The cash view — rent minus costs minus the full mortgage payment — tells you what actually lands in your account. The tax view is worked out differently, because interest isn't deducted and the capital part of a repayment mortgage never counts as a cost at all.
This is general information, not tax advice. Your position depends on how you hold the property (personally or through a company) and your circumstances — check GOV.UK or your accountant.
Know which is which
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Cash profitRent − running costs − full mortgage payment. What you can actually spend.
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Taxable profitInterest not deducted; a 20% credit applies instead; capital repayment isn't a cost. What HMRC taxes.
Confuse the two and a property can look profitable on paper while draining cash — or the reverse.
The average hides the loser
Add every property together and the portfolio can look fine while one door quietly bleeds money — the winners paying for the loser you can't see. Per-property profit is the only way to find it.
Which door to remortgage
The property whose profit a rate change would swing the most — you can only spot it per door.
Which door is draining you
Repairs, voids or a bad rate can turn one property negative. Per-property profit shows it before the year-end does.
Which door to let go
If a property never earns its keep, the number tells you plainly — instead of a hunch you keep ignoring.
One number per door — worked out for you
You could keep this sum in a spreadsheet for every property, every month. Or you can let software do it. Monkey Riot reads your rent statements and invoices, does the per-property maths, and turns it into one score per door — the Property Efficiency Score.
Every door, ranked
See net profit for each property side by side — the winners and the one that needs attention.
Feeds itself from Gmail
Connect Gmail read-only and rent and invoices flow into the right property, so the number stays current.
The Property Efficiency Score
The whole per-door calculation, distilled into a single figure you can act on at a glance.
Imports your file as-is
Bring the spreadsheet you already keep — messy is fine — and your history comes with you.
Digital records by default
The same records that answer "which door makes money" are the ones Making Tax Digital asks you to keep.
Refinance, fix or sell
With profit clear per door, the next move stops being a guess and becomes obvious.
Profit questions, answered
How do you calculate net profit on a rental property? +
Start with the rent you actually received for that property, subtract its running costs (letting and management fees, insurance, repairs, safety certificates, service charges, void periods and so on), then subtract the mortgage cost. What's left is the net profit for that door. Do it one property at a time — a portfolio total hides the property that's losing money.
Is mortgage interest tax deductible for landlords? +
For most individual landlords, no — not as a straight expense. Since April 2020, mortgage interest can no longer be deducted from rental income; instead you get a basic-rate (20%) tax credit on the interest. So your cash profit and your taxable profit are two different numbers, and the capital part of a repayment mortgage is never an expense. This is general information, not tax advice — check GOV.UK or your accountant for your position.
What counts as an allowable expense on a rental property? +
Typical allowable running costs include letting and management fees, landlord insurance, repairs and maintenance (not improvements), ground rent and service charges, safety certificates, accountancy fees and the cost of void periods. Rules change and there are exceptions, so use GOV.UK's guidance or an accountant to confirm what applies to you.
Why look at profit per property instead of the whole portfolio? +
A portfolio average can look healthy while one property quietly runs at a loss — the winners subsidise the loser and you never see it. Working out net profit per door is the only way to know which property to refinance, fix or sell first. That per-property view is exactly what Monkey Riot is built to give you.
How do I know which of my properties makes the most money? +
Line every property up on the same net-profit-after-the-mortgage basis and rank them. Monkey Riot does this automatically: it reads your rent statements and invoices, works out net profit per property, and turns it into one score per door — the Property Efficiency Score — so you can see at a glance which door makes you money and which one to deal with next.
Related guides
The spreadsheet alternative for landlords
Why Excel breaks at 4–25 properties, and how to switch without re-typing a thing.
MTD for landlords
What Making Tax Digital means for your records, deadlines and software.
See the Property Efficiency Score
One number per door — net profit after the mortgage, worked out for you.
This page is general information for UK landlords, not tax or financial advice. Tax treatment depends on your circumstances and how you hold your properties, and the rules can change. Always check the current guidance on GOV.UK or speak to a qualified accountant before making decisions.