Check the Rent Passes a Lender’s Test Before You Make an Offer
Most landlords work out whether a deal stacks up by comparing the rent with the mortgage payment. Lenders do something different. They take the interest at a higher stress rate and ask the rent to exceed it by a set margin, and a deal that looks comfortable on a spreadsheet can miss that margin by a few hundred pounds a month. This calculator applies the same test and then adds the cash you need to put in, your yield and your monthly cashflow. You can use it for a purchase or a remortgage, in your own name or through a company, and see where the numbers land before paying for valuations and legal work. Our guide on how buy to let mortgages are assessed covers the full process.
Buy to Let Mortgage Calculator UK
Test rental cover, borrowing, Stamp Duty, yield and cashflow for a buy to let purchase or remortgage.
Get a formal quote
Happy with the figures? Open the form below and your results are added to the message box for you. Add your details and anything else we should know, send it, and an adviser will come back with lender options and a formal quote.
How to Use the Buy to Let Mortgage Calculator
Choose purchase or remortgage at the top, and the boxes underneath adjust to match. A purchase needs the price and the deposit you plan to put in, while a remortgage needs the property value, the balance you still owe and any extra money you would like to raise.
Next comes the ownership. Buying personally and buying through a limited company are tested against different cover figures. A personal buyer also picks a tax band. If you already hold other mortgaged buy to lets, enter the number, because four or more can put you into portfolio landlord territory and lenders then ask for a schedule of your properties.
The mortgage section holds the rate, the fixed period, the term, the repayment type, the arrangement fee and the legal costs. Leave the illustrative rate in place until you have a quote.
Rent and running costs finish the form. Compare your rent with similar properties nearby before relying on it, since every result below depends on that figure. Void periods, the letting fee, maintenance and any service charge come off the rent before the mortgage payment is paid.
How Buy to Let Lenders Test the Rent
A lender does not compare the rent with the payment you will make. It works out the interest at a stress rate and wants the rent to beat that figure by a margin. For a limited company or a basic-rate taxpayer the margin is commonly 125 percent, and for a higher-rate taxpayer in their own name it is commonly 145 percent. Each lender picks its own number, and the calculator lets you override both.
The fixed period decides the stress rate. Many lenders test a two-year fix at the higher of 5.5 percent or your rate plus two percentage points, while a five-year fix is usually tested at your actual rate or close to it. The calculation uses interest only even when you choose a repayment mortgage.
Fix length alone can therefore turn a pass into a fail on the same property, and the worked example below shows exactly that.
How Much Can You Borrow on a Buy to Let Mortgage?
Your salary plays little part. The rent sets the ceiling, and the calculator works backwards from it to show the biggest loan the rent will support at the stress rate and cover figure in use.
Loan to value sets a second ceiling. Most lenders stop at 75 percent for buy to let, which is a 25 percent deposit, and the smaller of the two figures applies. When the rent produces the smaller figure, extra deposit or extra rent are the ways to unlock more.
A remortgage adds another line to the results: how much more the rent could support, which helps if you want to release cash for another purchase or for improvements.
Personal Name or Limited Company?
The ownership choice changes the cover a lender asks for, and the results show the rent needed on each basis, 125 percent for a company or basic-rate taxpayer and 145 percent for a higher-rate taxpayer in their own name.
Everything above concerns the mortgage. Tax depends on your own position, and an accountant is the right person to ask. If a company is on your shortlist, our guide to buying through a limited company explains special purpose vehicles, personal guarantees and what lenders look for in the directors.
Stamp Duty on a Buy to Let
In England and Northern Ireland a buy to let purchase pays the standard residential rates plus an extra 5 percent across the whole price, because the home is an additional property or a company is the buyer. On a £250,000 flat the standard rates give £2,500 and the extra 5 percent gives £12,500, which totals £15,000.
Scotland and Wales run separate taxes at different rates, and the calculator covers England and Northern Ireland only. A company buying a home above £500,000 may meet a further rate unless a relief applies, which is worth raising with an adviser before you commit.
Yield and Cashflow
Gross yield divides a year of rent by the price. Net yield works from the rent left after void periods, the letting fee, maintenance and any service charge, and it gives a truer picture of what the property earns.
Cashflow is the amount left each month once the mortgage has been paid, before tax. The calculator also shows the payment and the cashflow if rates rose by one point and by two points, which gives you a feel for the cushion in the deal. A property can clear a lender’s test and still leave very little each month, so look at both figures.
Worked Example: A £250,000 Flat
Imagine a £250,000 flat let at £1,250 a month and bought in your own name by a basic-rate taxpayer. A 25 percent deposit of £62,500 leaves a loan of £187,500, interest only at 5.79 percent.
Put it on a two-year fix and the lender tests it at 7.79 percent. Interest at that rate comes to £1,217 a month, and 125 percent of that is £1,521 of rent. With £1,250 coming in, cover reaches only 103 percent and the case fails. The rent supports a loan of £154,000, and the difference of £33,500 would have to come from extra deposit.
Choose a five-year fix tested at 5.79 percent and the picture changes. Interest is £905 a month, the rent required drops to £1,131 and £1,250 gives 138 percent cover, which passes. The flat, the rent and the deposit have not moved.
The cash side comes to £83,750 once you add the £62,500 deposit, £15,000 of Stamp Duty, a £3,750 arrangement fee at 2 percent and £2,500 of legal costs. After a 5 percent void allowance, 10 percent management and £100 a month for maintenance, the rent leaves £969 before the mortgage, and interest of £905 takes monthly cashflow down to roughly £64. The gross yield is 6 percent and the net yield 4.65 percent. This rent could support a stress rate of up to 6.4 percent, and a one-point rise in rates would push cashflow below zero.
More Examples to Try
Take a £325,000 flat with a 25 percent deposit and £1,700 of rent. The loan is £243,750 and the deal looks comfortable until the stress test arrives. On a two-year fix the stress interest of £1,523 calls for £1,904 of rent, and £1,700 gives only 112 percent cover. That fails, and the rent supports about £217,600, leaving roughly £26,150 to find in deposit. On a five-year fix the stress interest drops to £1,117, the rent called for is £1,396 and cover rises to 152 percent.
Back on the £250,000 flat with a five-year fix, cut the rent to £1,200. A limited company needs £1,131 and has 140 percent cover in hand. A higher-rate taxpayer in their own name needs £1,246 and falls short, with about £6,900 of extra deposit or rent nearer £1,250 needed to pass.
For a remortgage, imagine a £300,000 property with a £150,000 balance and £1,100 of rent on a five-year fix. Cover is 160 percent today and the rent supports about £192,000, which leaves roughly £42,000 to raise. A loan to value limit of 75 percent would permit £225,000, but the rent is the tighter limit here.
What the Calculator Cannot Tell You
Each lender builds its own affordability model. One may use a different stress rate, another will accept top slicing, where personal income covers a shortfall in the rent, and some will decline certain properties altogether. HMOs, multi-unit blocks and homes with a poor energy rating are assessed differently, and your credit record and experience as a landlord also count.
Several costs sit outside the calculator, among them tax, landlord insurance, safety certificates and tenant referencing. A whole-of-market broker can compare lenders, find which will accept the property and the structure, and tell you what to change before you apply.
Frequently Asked Questions
How accurate is a buy to let mortgage calculator?
It gives a sound first estimate of a deal.
Every lender applies its own stress rate and cover ratio, and the final figures usually move a little once a lender has looked at the case.
How much rent do I need for a buy to let mortgage?
The rent has to beat the interest at the lender’s stress rate by 125 percent for a company or basic-rate taxpayer, and by 145 percent in many cases for a higher-rate taxpayer in their own name.
Enter your loan and the calculator shows the exact rent needed.
Does this calculator include all the costs?
It covers the mortgage, Stamp Duty in England and Northern Ireland, the arrangement fee, legal costs and your running costs, and it reports yield and cashflow before tax.
Landlord insurance, safety certificates and your own tax bill fall outside it and need a separate budget.
What deposit do you need for a buy to let mortgage?
Around 25 percent, which is a loan to value of 75 percent.
A few lenders go lower and others ask for more when the rent is tight or the property unusual, and a bigger deposit tends to bring a lower rate.
How much can I borrow on a buy to let mortgage?
The rent and the loan to value limit decide it, and the smaller of the two figures is the ceiling.
The calculator shows the largest loan your rent supports.
Do buy to let mortgages have to be interest only?
No, although most borrowers choose it because the lower payment helps the rent pass the test.
A repayment mortgage is possible with a higher payment and thinner cashflow, and lenders still test the rent on an interest-only basis.
Can I use the calculator for a remortgage?
Yes.
Switch the mode to remortgage, enter the value, your balance and any extra to raise, and the results show the cover, the new loan to value and how much more the rent could support.
Does the calculator work for a limited company?
Yes.
Choose limited company as the buyer and the usual company cover figure applies. Directors are normally asked for personal guarantees, which leaves a personal side to the borrowing.
Final Thoughts
Use the calculator to get the numbers straight, then speak to us before you commit. We can compare the whole market and tell you which lenders suit the property and the way you plan to buy it.
UK Mortgage Broker is a whole-of-market broker helping clients throughout the UK and globally to secure funding on UK property. We are directly authorised and regulated by the Financial Conduct Authority. Your property may be repossessed if you do not keep up repayments on a loan secured against it. Buy-to-let and other business-purpose lending is not regulated by the Financial Conduct Authority.
Call: +44 1628 969 500
Email: info@uk-mortgagebroker.co.uk
Related Pages
- Buy-to-Let in 2026: What the Market Really Looks Like for Landlords – current market conditions, rates and landlord strategy.
- UK Mortgage Trends 2026 – rates, affordability and the buy to let outlook for landlords.
- How to Get a Buy-to-Let Mortgage with a Low Deposit – options when your deposit is below the standard 25%.
- Impact of Energy Efficiency (EPC) Requirements on Buy-to-Let Lending Criteria – how a property’s energy rating can affect lender criteria for rental homes.
- Stamp Duty Land Tax – how Stamp Duty applies to property purchases, including the surcharge on additional homes.
- Current Mortgage Rates UK – rate ranges by LTV band including buy to let products.
- Types of Mortgage UK – fixed, tracker, interest-only and repayment options explained.