For landlords with fixed rates ending in the next six to 18 months, the useful response to market volatility is to establish what each property can afford, what refinancing would cost and when decisions need to be made.

Britain’s 30-year government bond yield moved above 6% on 1 October 2026, reaching its highest level since 1998. Reuters reported the milestone alongside withdrawals of residential mortgage deals priced below 5%.

Markets have already moved again: a Trading Economics market snapshot on 2 October showed the 30-year yield back below 6%. For a landlord approaching refinancing, the important question is how a different borrowing cost would affect the rental business. That requires the portfolio’s own figures and suitable mortgage options.

Understand which rate matters

The 30-year gilt yield measures long-term UK government borrowing costs. Fixed mortgage pricing normally draws chiefly on shorter wholesale swap rates, particularly the two- and five-year rates, together with lenders’ funding costs, risks and margins. Swaps help lenders manage interest-rate risk. The Bank of England’s explanation of mortgage pricing describes those additional influences. The gilt yield does not directly set an individual landlord’s mortgage rate.

Reuters quoted broker John Charcol’s Nicholas Mendes putting the two-year SONIA (Sterling Overnight Index Average) swap rate at 4.68%, up 27 basis points, or 0.27 percentage points, over a month. That was a wholesale-market observation reported on 1 October, not a retail mortgage offer. A borrower’s available terms depend on the property, loan-to-value, ownership, rental cover and lender criteria.

The Bank’s August Money and Credit release and effective interest-rate tables, published on 29 September, provide older context about lending and rates actually paid. They cannot establish the buy-to-let deal available to a particular landlord now. Household repayment examples also cannot substitute for calculations using a landlord’s own borrowing.

Map every expiry and its exposure

Build one schedule covering every mortgage, including those outside the immediate refinancing window. Record the fixed-rate expiry, current balance and rate, remaining mortgage term, lender, reversion rate, and whether payments are interest-only or capital-and-interest. Add a realistic current property value and calculate loan-to-value by dividing the secured borrowing by that value.

Alongside each loan, record rent actually received and non-finance costs, including management, insurance, service charges, maintenance and an allowance for voids. Date the figures and distinguish estimates from statements or invoices. The schedule should reveal both vulnerable individual properties and several fixes ending close together, when pressure on the portfolio’s cash reserves could accumulate.

Test cash flow and interest cover separately

Start with suitable products a broker confirms are available at the time of the review, recording the quotation date and all fees. Model the existing position, a replacement at the quoted cost, and clearly labelled higher-cost scenarios. A further one or two percentage points can be useful sensitivity tests; they are assumptions for planning, not predictions.

For interest-only borrowing, annual interest is the balance multiplied by the annual rate. Illustratively, a one-percentage-point increase on an unchanged £200,000 balance adds £2,000 a year, or approximately £167 a month, before fees and tax. A repayment mortgage requires a payment calculation using the remaining term and reducing balance.

For the cash-flow test, deduct operating costs and the full mortgage payment from rent, then allow for fees when payable, planned major works and the relevant tax payments. Test a void or repair bill alongside higher interest. Avoid assuming that a rent increase will automatically cover the gap, and check how much cash remains available across the whole business.

Interest cover is rent divided by interest for the same period, expressed as a percentage. The PRA’s buy-to-let underwriting framework addresses rental cover and affordability. Ask the broker which stress rate and coverage requirement apply to each option, including any relevant remortgage treatment. A positive cash balance does not establish lender acceptance, and passing an interest-cover test does not establish that the remaining income meets your needs.

Compare the whole cost and the timetable

Compare suitable options over the same realistic holding period. Include interest, product fees, valuation, legal and broker costs, existing early-repayment charges and any exit charges that would arise under the intended plan. Fees added to the loan increase the balance and may attract interest. For repayment borrowing, compare the remaining debt as well as the monthly outlay.

Check when early-repayment charges reduce or end, and ask about application lead times, offer validity and completion requirements. Establish the terms for reserving or changing a product where available, and the cost of any gap after the existing fix expires. A fix ending in 18 months calls for preparation and monitoring; it does not establish that a replacement can be secured now.

Give the broker the business context

Prepare recent mortgage statements, tenancy agreements, evidence of rent received, property details and the portfolio schedule. Ask which accounts, tax records, bank statements, company information, licences, valuations or business plan the lender will require. Explain planned sales, improvements, capital needs and the income you want the portfolio to provide, because those plans affect the usefulness of a mortgage’s term and flexibility.

Property118’s earlier report on falling landlord purchase mortgage searches provides background on broker-platform activity, rather than completed lending or individual eligibility. The decision here remains specific to the owner: compare refinancing, a product transfer where available, reducing debt and retaining the existing arrangement until its agreed expiry.

For related help with a refinance or wider funding decision, read Property118’s guide to buy-to-let mortgage portfolio reviews. Obtain regulated mortgage advice where required, and have availability, criteria and total costs checked when making a decision. The purpose of the review is to understand the choices and their consequences; the market move does not determine the right choice for every landlord.