The risks of buy to let: common pitfalls to check before you invest

1.Is buy to let really passive income?

Not usually. A rental is closer to a part time business than a hands-off investment, and believing it runs itself is the single biggest misconception that lets every other risk here catch people off guard.

Buy to let is often sold as money for nothing: buy a flat, find a tenant, collect the rent. In practice it is closer to a part time business. You are responsible for finding and referencing tenants, gas and electrical safety certificates, repairs and emergency call outs, deposit protection, chasing late rent, an annual tax return, and keeping up with rules that change often.

You can pay a letting agent to handle the day to day, usually around 10 to 15 percent of the rent for full management, but that comes off your return and you are still the one carrying the risk and signing off the bills. The landlords who struggle are usually the ones who budgeted for none of this because they thought the property would look after itself.

2.Can a buy to let property fall in value?

Yes. Capital growth is not guaranteed, and some properties are more exposed than others.

House prices do not only go up. They move in cycles, and if you buy near the top and need to sell in a dip, you can get back less than you paid. The risk is sharper with new build flats, where part of what you pay is a developer premium that can fade once the building is no longer new, much like driving a new car off the forecourt.

If the value falls below what you owe, that is negative equity, and it makes the property hard to sell or remortgage without putting in more cash. New build and leasehold flats can be hit twice here, because cladding and building safety issues have made some of them very difficult to sell or value at all.

3.What is the buy to let remortgage trap?

Rolling fees into the loan and a small dip in value can quietly push you into a worse deal at renewal.

Most buy to let mortgages are fixed for two or five years, then you remortgage onto a new deal. Two things can go wrong at that point. Product fees are often added to the loan rather than paid up front, so the balance creeps up each time you switch. And if the property value has dipped, your loan to value rises, which can move you into a higher rate band or leave you unable to remortgage at all.

When a remortgage is not possible, you usually drop onto the lender's standard variable rate, which tends to be a lot higher and can turn a small monthly profit into a monthly loss.

4.What are the risks of an interest only buy to let mortgage?

Most buy to let mortgages are interest only, so the debt does not reduce on its own.

With an interest only mortgage you pay the interest each month but not the capital, so the balance you owe stays the same for the whole term. That keeps monthly payments lower, which helps cash flow, but it leaves a question for the end of the term: how does the loan get repaid?

The unspoken assumption is usually "I will sell the property and clear it." That works when values have risen, but if prices are flat or down when the term ends, the sale may not cover the loan and you are left to find the shortfall. Relying entirely on capital growth to repay the debt is one of the quieter risks in buy to let.

5.Can a buy to let fail the lender stress test when rates rise?

A deal that stacked up at low rates may not pass the lender's test at renewal.

Lenders do not just check that the rent covers the mortgage today. They apply a stress rate, a higher assumed interest rate, and require the rent to cover the payment at that higher rate by a set margin, known as the interest cover ratio. When rates rise, or when you have not increased the rent for years, the same property can fail that test even though it is comfortably profitable at the actual rate.

If the rent no longer passes, you may not be able to borrow the same amount at renewal, which forces you to either put in cash to reduce the loan or accept a worse deal. Checking the rent against a realistic stress rate before you buy is one of the most useful things you can do.

6.What running costs do landlords underestimate?

Gross yield looks great until the real costs come out of it.

It is easy to model the rent against the mortgage and call the difference profit. The gap between that and reality is the costs that do not show up until they happen:

• Void periods when the property sits empty between tenants, with no rent but the mortgage still due.
• Maintenance and the occasional big bill, a boiler, a roof, an electrical fault.
• Letting agent fees if you are not managing it yourself.
• Landlord insurance, which is not the same as ordinary home insurance.
• The stamp duty surcharge on the purchase, which adds a meaningful sum on top of standard rates for an additional property.

A useful habit is to budget for the property to be empty for a few weeks a year and to keep a cash buffer for repairs, rather than assuming twelve months of rent with nothing going wrong.

7.How much does a bad tenant actually cost?

The problem is rarely just the missed rent. It is how long and how much it takes to put right.

A void is not only lost rent. While the property is empty you usually pick up the council tax and utility bills, and you may pay a fee to find the next tenant. And if a tenant stops paying and will not leave, regaining possession through the courts can take several months and run to a few thousand pounds in legal and court costs, all while no rent is coming in.

Recent reforms have also changed the maths on arrears. The threshold and notice periods for some possession routes have lengthened, which can mean a non paying tenant costs more before you are able to act. This is one reason a cash buffer matters: it is what carries the property through a bad stretch.

8.What are the leasehold cost risks with a flat?

With a flat, costs you do not control can wipe out the profit even if the value holds.

If you buy a leasehold flat, you take on the ground rent and the service charge, and neither is fully within your control. Ground rent on some older leases is set to rise sharply over time, and service charges can jump when major works are planned. A building wide repair billed through a Section 20 process, or cladding remediation, can land each flat owner with a bill running into thousands.

9.How has tax reduced buy to let returns?

The tax treatment of buy to let is less generous than many people assume, particularly for higher earners.

If you hold a property in your own name, you can no longer deduct mortgage interest from your rental income before tax. Instead you get a tax credit worth 20 percent of the interest, a change often called the Section 24 rule, which can leave higher rate taxpayers paying more than they expect, and in some cases tax on income they have not really made. When you eventually sell, capital gains tax may apply to the profit, and the tax free allowance has been reduced in recent years.

Some landlords hold property through a limited company to change how this works, but that brings its own costs and admin and is not automatically better. This is very much a question for a tax adviser.

10.How often do the rules for landlords change?

Being a landlord now comes with a moving set of legal duties, and the direction of travel is more regulation, not less.

Recent reform has reshaped how tenancies and possession work, and energy efficiency standards for rented homes have been tightening, which may mean spending money to improve older properties to keep letting them. None of this makes buy to let impossible, but it does mean you cannot set it and forget it. Staying compliant is part of the job, and the cost of upgrades and compliance should be in your plan rather than a surprise.