Buy-To-Let Mortgage Tips – Which Mistakes Do Landlords Make?

A buy-to-let mortgage is a specialised loan designed for purchasing property to rent out rather than live in, assessed primarily on rental income potential rather than personal earnings.

The good news for buy-to-let investors is that demand for rental units is strong in the current property market. However, rising interest rates (2022 to 2024), tax changes, and stricter lending rules have made property investment more challenging than before.

We’ve compiled these buy-to-let mortgage tips to help first-time investors, experienced operators expanding, homeowners considering renting out their property, and anyone considering property investment. We focus specifically on mistakes to avoid when applying for a BTL mortgage.

What’s the Difference between a Buy-to-Let and Residential Mortgage?

The core difference between buy-to-let and residential mortgages is that BTL loans are assessed on the property’s rental income, rather than personal earnings.

Other differences include:

• Higher deposit: BTL mortgages sometimes require a deposit of up to 40%.
• Rental stress tests: Lenders perform stress tests to check that projected monthly rental income covers mortgage repayments at “stressed” (higher) interest rates.
• Interest-only options: Many landlords choose interest-only mortgages to keep monthly costs low.

Common Mistakes When Applying for Buy-to-Let Mortgages

Following the 2008 financial crisis, lenders tightened their buy-to-let mortgage rules.

Today, BTL lending criteria remain strict due to factors like sharply rising interest rates, higher living costs, and regulatory challenges.

Property investors must submit mortgage applications that are completely accurate and thoroughly prepared. Even the smallest errors can damage your approval chances, so understanding common pitfalls helps protect your investment plans.

1.    Failing the Affordability Stress Test

Mortgage providers want assurance that your property’s rental income will cover loan repayments today and in the future, so they apply a stress test using higher hypothetical interest rates.

Stress tests typically require the expected rental income to cover 125% to 145% of the mortgage repayments, calculated at stressed rates (often up to 8%+).

Tip: Calculate your potential rental yield conservatively by dividing annual rental income by property value. Run your own stress test by checking how your conservative rentals cover payments at higher interest rates. Chat to a qualified mortgage advisor for further guidance.

2.    Underestimating costs

Underestimating costs is one of the main reasons for losses on buy-to-let properties. It’s vital to consider all “hidden” costs of buying a house to evaluate your buy-to-let investment properly. Full accounting also shows your lender you’ve done your homework.

Factor in:

• Stamp duty surcharge
• Conveyancing/ legal fees
• Valuation fees and mortgage costs
• Property upgrade and repairs
• Setting up utilities (including Wi-Fi)
• Maintenance costs
• Letting agent fees
• Insurance
• Periods without tenants (voids)

Tip: Prepare a detailed budget that includes the property’s purchase price and associated fees, plus all management, maintenance, and contingency costs.

3.    Insufficient Deposit or Weak Credit Profile

In most cases, BTL mortgages require a larger deposit than residential loans. Funders also look closely at your credit record.

• Deposit: Expect to put down from 20% to 40%. On the plus side, a larger deposit often secures a better interest rate.
• Credit: A strong credit score is also essential. Any recent missed payments or high levels of personal debt will weaken your application.

Tip: Save realistically for your deposit. Work proactively on your credit score by paying down loans, avoiding new debt, and checking your credit report for errors.

4.    Choosing the Wrong Mortgage Type

Many BTL landlords default to an interest-only fixed rate mortgage because it maximises cash flow. However, you need a viable repayment strategy to settle the full principal debt at the end of the term.

Tip: Consider your long-term goals. If you plan to hold the property long-term, an interest-only loan may work. But if you want to reduce debt or sell sooner, a repayment mortgage might be wiser. Also factor in your income tax position and potentially higher variable rate payments at the end of a fixed contract.

5.    Ignoring Tax and Regulatory Changes

There are several challenging regulatory developments landlords must prepare for:

• Section 24: This legislation phased out 100% mortgage interest tax relief for landlords, replacing it with a basic rate tax credit of 20%.
• EPC C: From 2030, all privately rented properties must achieve a minimum Energy Performance Certificate rating of C. This could entail costly upgrades.
• Renters’ Rights Bill: This bill proposes to abolish Section 21 “no-fault” evictions and introduce open-ended tenancies (giving tenants greater rights).
• Making Tax Digital (MTD) for Income Tax: This new tax rule will require many landlords to file quarterly returns with HMRC from April 2026.

Tip: Get proper tax and legal advice from professionals who specialise in property investment before purchasing a property.

Is Buy-to-Let a Good Investment in 2026?

“Should I buy to let?” We hear this question every day.

The short answer is: “It depends.”

High house prices have made homeownership difficult, keeping rental demand strong. However, fluctuating interest rates, potential EPC-related costs, less tax relief, and additional admin are squeezing BTL margins.

Carefully consider the tenant demand and capital growth prospects in your location. For energy-compliant properties in favourable locations, BTL remains a good investment, especially if backed by sound finances and admin controls.

How to Avoid Losing Money on Rental Property

Follow these 4 strategies to protect your rental property investment and avoid operating at a loss:

1. Be conservative: When calculating your rental yield, be conservative about your income and realistic about your costs.
2. Due diligence: Thoroughly research the local market demand and the cost of necessary property improvements before committing to a purchase.
3. Factor in common risks: Ensure your projected income can withstand risks like void periods, unexpected large repairs (e.g., boiler replacement), and interest rate hikes.
4. Build a financial buffer: Maintain a cash reserve of at least six months of mortgage payments, covering expected maintenance and void periods.

Expert Advice for Buy-to-Let Landlords

To help you compare and secure the best BTL mortgage deal, why not speak to an independent mortgage advisor?

We offer expert, personalised advice to both experienced BTL businesses and young professionals just entering the market. Flagstone is an independent broker with access to the entire market, plus insider knowledge of lenders’ stress test calculations.

Get in touch with our mortgage broker team and let us find you great exclusive rates.

YOUR BUY TO LET PROPERTY MAY BE REPOSSESSED OR A RECEIVER OF RENT APPOINTED IF YOU DO NOT KEEP UP REPAYMENTS ON YOUR MORTGAGE.