A landlord in Manchester once told me she worked out her numbers on a napkin before buying her first rental flat. Rent minus mortgage payment. Simple. Six months later, a boiler died, a tenant left without notice, and she realised her napkin math had missed almost half the real costs of owning that property.
That’s the thing about buy to let mortgage — they look straightforward from the outside. Find a property, put down a deposit, rent it out, collect the difference. In reality, the lending, the tax, and the day-to-day running costs work differently to a normal homeowner mortgage, and the gap between “looks profitable” and “is profitable” catches a lot of first-time landlords off guard.
This guide walks through the nine things that matter most if you’re weighing up a buy to let purchase in 2026 — plus the mechanics of how the mortgage itself works.
A quick note before we start: mortgage rates, lending rules and tax thresholds shift regularly. Treat the numbers here as illustrations, not quotes, and check current terms with a lender, broker or tax adviser before you commit to anything.
What Is a Buy to Let Mortgage?
Put simply, it’s a mortgage for a property you plan to rent out rather than live in. The steps look familiar — find a property, put down a deposit, borrow the rest, pay it back monthly — but the way lenders judge your application is different.
A residential mortgage lender mostly cares about your salary. A buy-to-let lender cares just as much, sometimes more, about what the property itself will earn in rent.
1. Expect to Put Down a Bigger Deposit
The first surprise for most new landlords is the deposit size. Where a residential mortgage might ask for 10% or even 5% down, buy-to-let lenders typically want around 25%.
Take a £250,000 property:
£250,000 × 25% = £62,500 deposit, leaving a £187,500 mortgage.
Some lenders will go lower, some will ask for more depending on the property type or your circumstances. But the direction of travel is the same — you’ll need more cash upfront than you would buying a home to live in.
This deposit size also sets your loan-to-value (LTV):
- 25% deposit → 75% LTV
- 30% deposit → 70% LTV
- 40% deposit → 60% LTV
A lower LTV generally opens the door to better rates, because you’re a lower-risk borrower in the lender’s eyes.
2. Rental Income Matters as Much as Your Salary — Sometimes More
With a residential mortgage, the question is: can you afford this? With buy-to-let, the question shifts to: can the property afford this?
Lenders run what’s called a rental stress test — checking whether the expected rent comfortably covers the mortgage payments, usually calculated at a higher interest rate than you’re actually being offered. It’s their way of building in a safety margin.
Here’s where it trips people up: a property can look perfectly affordable at today’s rate and still fail this test, because the lender is stress-testing against a rate that doesn’t exist yet. If the numbers are tight, this is often the first hurdle, not the deposit.
3. The Mortgage Payment Is Only Part of the Bill
New landlords tend to do this sum: rent minus mortgage payment equals profit. It’s rarely that clean.
A rental property also comes with letting agent fees, insurance, repairs, gas safety checks, ground rent, licensing costs, accountant fees, and the occasional month where nobody’s paying rent at all.
Say a property brings in £1,400 a month. If mortgage interest, maintenance, insurance and the rest add up to £1,000, you’re left with £400 — before tax. Not £1,400. That distinction matters enormously when you’re deciding whether a deal actually stacks up.
4. Most Buy-to-Let Mortgages Are Interest-Only
Unlike a typical homeowner mortgage, a large share of buy-to-let deals are interest-only. Your monthly payment covers just the interest, not the loan itself, which keeps payments lower.
The catch is obvious once you say it out loud: you still owe the full amount at the end. Borrow £180,000 interest-only, and £180,000 is still sitting there when the term ends, unless you’ve got a plan to clear it — selling, refinancing, savings, or switching to a repayment mortgage.
“The property will just go up in value” isn’t a repayment strategy. It’s a hope.
5. Tax Rules Can Quietly Eat Into Your Return
This is the part landlords most often underestimate. For individually-owned rental properties, mortgage interest isn’t deducted from rental income the way it once was — instead there’s a basic-rate tax reduction applied under current rules. For higher-rate taxpayers, that shift can meaningfully dent the numbers.
Tax also touches almost every stage of owning a rental property — buying it, earning rent from it, selling it, passing it on, or running it through a limited company instead of your own name. Each route has different implications.
This is genuinely one area where a conversation with a qualified tax adviser before you buy is worth more than any article, including this one.
6. Stamp Duty Adds a Real Cost Before You Even Own the Property
Buying an additional residential property — which a buy-to-let almost always is — typically triggers a higher rate of Stamp Duty Land Tax in England and Northern Ireland compared with buying your only home. Scotland and Wales run their own separate systems, so don’t assume England’s rules travel with you.
This isn’t a small line item. It should be part of your budget from the very first calculation, not something you discover at the solicitor’s stage.
7. Empty Months Can Wreck Your Cash Flow Fast
A rental property doesn’t come with a tenant guarantee. Void periods — stretches with no one paying rent — are one of the quiet risks that catch out landlords who’ve only budgeted for the good months.
If your mortgage and running costs total £1,000 a month and the flat sits empty for two months, that’s £2,000 gone with nothing coming in to offset it. A boiler replacement or an insurance claim landing in the same stretch makes it worse.
An emergency fund isn’t optional here — it’s the difference between a manageable setback and a genuine financial problem.
8. You’re Legally Responsible for More Than You’d Think
Being a landlord comes with obligations that have nothing to do with mortgages or rent. Gas safety checks, electrical safety, smoke and carbon monoxide alarms, deposit protection schemes, energy efficiency standards — the list is long, and it varies depending on where in the UK the property sits.
Properties let as houses in multiple occupation (HMOs), or those in areas with local licensing schemes, often carry extra requirements on top. These rules also change over time, so relying on a checklist from a few years back is a real risk. Check current government and local council guidance rather than assuming yesterday’s rules still apply.
9. The Lowest Rate Isn’t Automatically the Best Deal
It’s tempting to sort mortgage comparisons by interest rate and stop there. But the headline rate is one line in a bigger sum.
Arrangement fees can run into thousands. Early repayment charges can bite if you refinance sooner than planned. Valuation and legal costs add up before you’ve even drawn down the loan. And two mortgages with identical rates can behave very differently depending on the term length and whether overpayments are allowed.
The right mortgage is the one that fits your actual plans for the property — not necessarily the one at the top of a comparison table.
How a Buy to Let Mortgage Actually Works, Step by Step
Step 1 — Work out your real budget. Deposit, stamp duty, mortgage fees, legal costs, survey, repairs, and a cash buffer for the unexpected. Not just the deposit.
Step 2 — Research the rental market properly. Local demand, average rents, tenant demographics, transport links, nearby employment. A high headline rent on a property that’s overpriced for the area isn’t actually a good deal.
Step 3 — Calculate the rental yield. Gross yield is a starting point: annual rent divided by property value, times 100.
Annual rent of £15,000 on a £250,000 property gives you:
£15,000 ÷ £250,000 × 100 = 6%
Gross yield ignores mortgage interest, maintenance, insurance and tax, though — it’s a headline number, not the real return. Net yield, after costs, tells the fuller story.
Step 4 — Compare mortgage options properly. Rate, LTV, fees, term, fixed period, early repayment charges, and how the lender’s rental stress test treats your numbers. A broker who works specifically in buy-to-let lending can be worth the fee here.
Step 5 — Apply. The lender will look at your income, existing debts, credit history, the property’s value, expected rent, and — depending on the lender — your track record as a landlord if you have one.
Rental Yield and Loan-to-Value, Explained Properly
Gross rental yield tells you how much a property earns annually relative to its price. Take a £300,000 property renting for £1,500 a month:
£1,500 × 12 = £18,000 a year
£18,000 ÷ £300,000 × 100 = 6%
That 6% is not your profit margin — it’s before every cost is subtracted.
Loan-to-value (LTV) compares your mortgage to the property’s value. A £225,000 mortgage on a £300,000 property:
£225,000 ÷ £300,000 × 100 = 75% LTV
The remaining 25% is your deposit or equity. LTV matters because lenders price mortgages differently at different LTV bands — the more equity you hold, the more competitive your options tend to be.
Can First-Time Landlords Get a Buy to Let Mortgage?
Yes — plenty of lenders will work with someone buying their first rental property. What changes is the range of lenders available to you, since some providers set minimum income requirements or prefer applicants with existing landlord experience. It’s worth shopping around rather than assuming every lender applies the same criteria, because they don’t.
Can You Live in a Property Bought With a Buy-to-Let Mortgage?
No — not without checking with your lender first. Buy-to-let mortgages are underwritten on the assumption the property will be tenanted, not owner-occupied. If your circumstances change and you want to move in yourself, that’s a conversation to have with your lender before you do it, not after.
Buy to Let vs Residential Mortgage
| Feature | Buy to Let | Residential |
|---|---|---|
| Purpose | Rental investment | Your own home |
| Who lives there | Tenants | You / your household |
| Rental income | Central to the assessment | Rarely a factor |
| Typical deposit | Larger | Varies widely |
| Interest-only | Common | Uncommon |
| Tax treatment | Different rules apply | Different rules apply |
| Legal obligations | Landlord duties | Homeowner duties |
What Happens If Interest Rates Rise?
If you’re on a variable rate, or your fixed deal is coming up for renewal, a rate rise hits your monthly costs directly. Say your mortgage balance sits at £200,000 — even a modest rate increase can push your monthly financing cost up meaningfully, and if your rent doesn’t move with it, your margin shrinks fast.
It’s worth stress-testing your own numbers before a lender does it for you. What happens if the mortgage gets more expensive? What if the flat sits empty for three months? What if a £5,000 repair lands out of nowhere? If any of those scenarios would sink you, the investment is more fragile than it looks on paper.
Is a Buy to Let Mortgage Worth It?
There’s no universal answer — it depends entirely on the numbers for your specific property, your tax position, and how much risk you’re comfortable carrying.
Done well, it can bring in rental income, long-term exposure to property, and a way to diversify beyond stocks and savings. Done without proper planning, it can just as easily mean a property that costs more to hold than it earns, especially once prices dip, rates rise, or a tenant leaves mid-lease.
Treat it as an investment decision that needs real numbers behind it — not a bet on house prices always going up.
Frequently Asked Questions
What is a buy to let mortgage? A mortgage for a property you intend to rent out, rather than live in yourself.
How much deposit do I need? Around 25% is typical, though it varies by lender, property and applicant.
Can first-time landlords get a buy to let mortgage? Yes, though the range of lenders willing to work with you may be narrower than for experienced landlords.
Can rental income cover the mortgage? It’s meant to, and lenders check for it — but there’s no guarantee it always will, especially during void periods or rate rises.
Are buy to let mortgages interest-only? Many are, though repayment options exist too.
Is buy to let profitable? It depends on the purchase price, rent achieved, financing costs, tax, maintenance and how often the property sits empty.
Do landlords pay tax on rental income? Yes, and the rules depend on your circumstances and how the property is owned. Speak to a tax adviser before buying.
Can I use a residential mortgage for a rental property? No — don’t assume this is allowed. Speak to your lender before letting out a property bought on a residential mortgage.
Final Thoughts
A buy to let mortgage gets you the property. It doesn’t guarantee the investment works. The landlords who do well tend to be the ones who ran the full numbers before buying — deposit, mortgage costs, realistic yield, tax, maintenance, and a buffer for the months that don’t go to plan — rather than the ones who assumed rent would always cover the bills and prices would always climb.
Run the numbers properly, check current rates and rules before you commit, and build in room for the year that doesn’t go as planned. That’s usually what separates a rental property that works from one that quietly drains money for years.
