When landlords compare buy-to-let mortgages, the interest rate is often the first figure they notice. That is understandable: even a relatively small difference in the rate can affect monthly payments and rental cash flow.
However, the mortgage with the lowest advertised rate is not necessarily the mortgage that will cost the least—or the one best suited to the landlord’s plans.
Arrangement fees, valuation costs, legal expenses, early repayment charges, incentives and lender criteria can all change the calculation. A mortgage that initially appears highly competitive may ultimately cost considerably more than an alternative with a slightly higher rate.
The objective should therefore be to find the right overall mortgage, not simply the lowest headline rate.
The rate is only one part of the cost
The interest rate determines how much interest is charged on the outstanding mortgage balance. It is clearly important, particularly where a landlord is borrowing a substantial amount.
But it should be considered alongside the other costs attached to the product.
These may include:
- A lender arrangement or product fee.
- A mortgage valuation fee.
- Legal and conveyancing costs.
- A lender’s administration or completion fee.
- A broker fee, where applicable.
- An existing lender’s early repayment charge.
- A mortgage exit or redemption fee.
- Additional costs associated with a limited company application.
- The cost of obtaining specialist property reports or valuations.
Some mortgage products include free valuations, assisted legal work or cashback. Others offer a lower rate but charge a substantial arrangement fee.
The only reliable comparison is one that brings all the relevant costs together.
A lower rate can still produce a higher total cost
Consider a landlord taking a £250,000 interest-only mortgage.
One product has an interest rate that is 0.25 percentage points lower than another. On an interest-only basis, that difference represents approximately £625 a year, or £1,250 over a two-year product period.
However, suppose the lower-rate mortgage has a 2% arrangement fee. On a £250,000 loan, that fee would be £5,000. If the alternative mortgage charged a fee of £999, the difference in fees would be £4,001.
In this simplified example, the interest saving offered by the lower rate would not compensate for the higher arrangement fee during the initial two-year period.
The precise result will depend on the loan amount, product period, interest rate, fees and whether those fees are paid upfront or added to the borrowing. If a fee is added to the mortgage, interest may also be charged on it.
This is why comparing rates without calculating the total cost can be misleading.
The size of the mortgage changes the calculation
A percentage-based arrangement fee can become particularly significant on a larger mortgage.
Conversely, a landlord borrowing a substantial amount may benefit more from a lower interest rate because the rate saving applies across a larger balance.
This means the same mortgage product will not represent equal value for every landlord. A product that works well for a £100,000 mortgage may be much less competitive—or considerably more attractive—on a £500,000 mortgage.
The comparison must therefore be based on the landlord’s actual borrowing requirement rather than a general mortgage table.
Consider the product period
Landlords should also decide how long they expect to retain the mortgage.
A two-year fixed rate may offer a shorter commitment, but the landlord could face another set of arrangement, valuation and legal costs when the mortgage is reviewed again. A five-year product may provide longer-term payment certainty, but it may also include early repayment charges lasting for much longer.
Neither option is automatically better.
The right product period may depend on whether the landlord expects to:
- Retain or sell the property.
- Carry out major refurbishment.
- Release equity later.
- Change the ownership structure.
- Increase or reduce the borrowing.
- Make substantial overpayments.
- Reorganise mortgages across several properties.
The mortgage should support the landlord’s wider property strategy, not restrict it unnecessarily.
Early repayment charges can change everything
An early repayment charge may apply if the mortgage is repaid, refinanced or substantially reduced before the agreed product period ends.
These charges are often calculated as a percentage of the outstanding balance. On a large mortgage, even a relatively small percentage can represent a considerable cost.
A landlord who expects to sell, refinance or restructure the property should therefore examine the early repayment charge period carefully. A lower rate may provide a modest monthly saving but create a much larger cost if the landlord needs to leave the product earlier than expected.
Flexibility can have a real financial value.
Lender criteria matter as much as pricing
The cheapest mortgage on a comparison table may not be available for the property or borrower concerned.
Buy-to-let lenders can take different approaches to:
- Rental stress testing.
- Minimum rental coverage.
- Loan-to-value limits.
- Houses in multiple occupation.
- Multi-unit properties.
- Flats above commercial premises.
- Holiday and short-term letting.
- Limited company borrowing.
- Landlords with several properties.
- Property condition and construction.
- Applicant income, experience and credit history.
A lender offering a slightly higher rate may provide a more suitable rental calculation, accept the proposed property type or allow the landlord to borrow the amount required.
An attractive rate is of no practical value if the application does not meet the lender’s criteria.
Do not overlook the reversion rate
Landlords should understand what happens when the initial fixed or discounted period ends.
Unless another arrangement is made, the mortgage will normally move onto the lender’s reversion rate. This can result in a significant increase in monthly interest costs.
The reversion rate should not determine the original mortgage choice on its own, because most landlords will review their options before the product ends. Nevertheless, it demonstrates why mortgage expiry dates should be monitored and why remortgage planning should begin early.
The best mortgage is the one that fits the complete plan
A proper comparison should consider:
- The interest payable during the product period.
- Every lender and transaction fee.
- Any cashback or other incentive.
- The cost of leaving an existing mortgage.
- The proposed mortgage term.
- The early repayment charge structure.
- The lender’s rental and property criteria.
- The landlord’s plans for the property.
- The likely need for future flexibility.
- The cost and implications of refinancing again.
This produces a much more meaningful assessment than simply placing two interest rates next to each other.
Let NetRent help you compare the complete mortgage
NetRent Mortgage Solutions works with DNA Financial Solutions to give landlords access to independent mortgage and finance advice.
The aim is not simply to identify an attractive headline rate. It is to find a mortgage that works for the property, satisfies the relevant lender criteria and supports the landlord’s wider plans.
If you are purchasing a rental property, approaching the end of an existing deal or reviewing mortgages across several properties, speak to us before making a decision.
Call 01352 721300 or email mortgages@netrent.co.uk.
NetRent does not provide legal advice. The content above represents our understanding of rental property law and market trends as at 18 August 2026. Mortgage products, interest rates, fees and lender criteria can change without notice. Individual circumstances vary, and appropriate professional advice should be obtained before making any financial, legal or tax decision.