Buy to Let Remortgage: What You Could Save

A buy-to-let remortgage calculator estimates whether moving to a new mortgage deal will actually save you money once the arrangement fee, any early repayment charge and the new rental cover test are all taken into account. The simplest version compares your monthly payment on the new rate against your current one; a proper calculation goes further and checks whether the property still passes the lender's interest coverage ratio (ICR) at today's rent and stress rate.

This guide walks through when remortgaging is worth doing, how to weigh fees against the rate saving, what changes on the ICR test compared with your original mortgage, and a worked example you can adapt to your own numbers.

When remortgaging pays

Most buy-to-let remortgages happen for one of three reasons: your fixed rate is ending and you want to avoid dropping onto the lender's standard variable rate (SVR), you want to release equity for another purchase or refurbishment, or a better rate has appeared that beats your current deal even after fees.

The first reason is the most common, and the least optional. SVRs are typically several percentage points above the fixed rate you were on, so doing nothing when a fix ends is rarely the cheapest option, even allowing for a new arrangement fee. Our guide on buy-to-let remortgaging covers the wider process, including timing and the documents a lender will want.

As a rule of thumb, it is worth running the numbers if any of the following apply:

Your current fix ends within the next six months.
Your existing rate is materially above what is currently available for your loan-to-value (LTV) and property type.
Your rental income or property value has changed enough that a lower-LTV product, with a better rate, might now be within reach.
You want to release equity, and the extra borrowing still comfortably clears the lender's rental cover test.

It is usually not worth remortgaging simply because a slightly cheaper headline rate exists elsewhere, if the fee difference and any early repayment charge (ERC) on your current deal would outweigh the saving over the fixed term. That is exactly the trade-off a calculator needs to check, not just the rate on its own.

Fees vs rate saving

The rate you see advertised is only part of the cost of a remortgage. To compare two deals properly, you need to look at the total cost over the fixed period, not just the monthly payment in isolation.

Costs to weigh up on the new deal:

Arrangement or product fee. Often one to three per cent of the loan, sometimes payable upfront and sometimes added to the loan balance. A fee added to the loan increases the amount you pay interest on for the whole term, so it is not free even if it feels that way at completion.
Valuation fee, if the lender charges one separately rather than including it in the product.
Legal fees, though many remortgage products include free legal work for a straightforward case.
Broker fee, if you are using one, though many buy-to-let brokers are paid by the lender instead.

Costs that might apply on exiting your current deal:

Early repayment charge (ERC), typically a percentage of the outstanding balance, charged if you remortgage before your current fixed or discounted period ends. This is usually the single biggest reason a remortgage that looks attractive on rate turns out not to be worth doing yet.
Exit or deeds release fee, a smaller administration charge most lenders apply when a mortgage is repaid.

A simple way to compare two deals is to add up the total cost of interest plus fees over the fixed term for each option, then compare the totals rather than just the headline rates. A lower rate with a high fee does not always beat a slightly higher rate with a low fee, particularly on a shorter fix or a smaller loan, where the fee makes up a larger share of the total cost. Our guide to buy-to-let mortgage rates covers what else drives pricing beyond the headline number.

ICR on remortgage

A remortgage is not simply a formality once you already hold a mortgage on the property. The new lender reassesses the deal from scratch, which means the rent has to clear the interest coverage ratio (ICR) test again, at the current stress rate and threshold, not the one that applied when you first bought.

This matters because stress rates and thresholds move over time, and your rent may not have kept pace with them. Two things commonly catch landlords out at remortgage:

Rent has not risen enough. If your rent has stayed flat while stress rates rose, the same property that passed easily a few years ago can now be tighter, or fail outright at the loan amount you want.
Your tax position has changed. A basic-rate taxpayer typically needs 125% ICR, while a higher-rate taxpayer borrowing in personal name typically needs around 145%, because Section 24 restricts higher-rate relief on mortgage interest. If your income has moved you into a higher tax band since you took out the original mortgage, the same rent may no longer clear the higher threshold. Our guide to ICR for buy-to-let explains how the calculation works and how personal versus limited company ownership changes the threshold.

If the property does not comfortably clear the ICR test at the loan amount you want, you generally have three options: reduce the loan by paying down some of the balance, look at a lender with a lower stress rate (often available on longer fixes), or move the property into a limited company structure, where the ICR threshold is usually lower regardless of your personal tax band. None of these is automatically right for every situation, and moving ownership structure in particular has tax consequences well beyond the mortgage itself.

Example

Take a property valued at £240,000 with an outstanding interest-only mortgage of £160,000 (67% LTV), currently on a two-year fix at 5.4% that is due to end in four months. The tenant pays £1,150 a month.

Staying on the lender's SVR (do nothing):

If the SVR is 8.2%, the monthly interest cost rises to £160,000 x 8.2% / 12 = £1,093.33, more than eight times the arrangement fee this landlord would pay on a new deal within the first year alone.

New two-year fix at 4.8%, £1,500 fee added to the loan:

New loan: £161,500. Monthly interest cost: £161,500 x 4.8% / 12 = £646.

Over 24 months, the saving compared with staying on the SVR is roughly (£1,093.33 - £646) x 24 = £10,720, comfortably clearing the £1,500 fee even before accounting for the extra interest on the £1,500 itself.

Checking ICR on the new deal:

At a 5.5% stress rate and 125% ICR (basic-rate taxpayer), the required rent is: £161,500 x 5.5% / 12 x 1.25 = £925.10. At £1,150 a month, this deal passes with room to spare.

If this landlord were a higher-rate taxpayer needing 145% ICR instead, the required rent would be £161,500 x 5.5% / 12 x 1.45 = £1,073.11, still below the actual rent of £1,150, so the deal would still pass, though with a narrower margin. This is the kind of gap worth checking explicitly rather than assuming, since a smaller rent or a higher stress rate could easily flip the result.

How Property HQ helps

Working through fees, ERCs and the ICR test by hand for every property coming up for renewal is manageable for one mortgage, but becomes time-consuming once you are tracking several fixed-rate end dates across a portfolio. Property HQ tracks each mortgage's fixed-rate end date, current rate and rent, flags when a remortgage window is approaching, and stress-tests rental cover against current thresholds so you know where you stand before you speak to a broker. If you hold four or more mortgaged properties, our portfolio landlord rules guide covers the extra underwriting a remortgage application is likely to involve.

Disclaimer

This guide is general information for UK landlords, not financial or mortgage advice. Rates, fees and lending criteria vary by lender and change over time. Speak to a mortgage broker or your lender, and check GOV.UK or HMRC guidance where tax treatment is relevant, before making a remortgage decision.