Three mortgage numbers every portfolio landlord should know

Published 16 August 2026 · Written by the Lar founder

There are three mortgage numbers every Scottish landlord running a portfolio should be able to answer without looking anything up.

Here they are, with the maths behind each one.

1. Your next fixed-rate expiry date and the SVR it reverts to

Most BTL mortgages in Scotland are on two-year or five-year fixed rates. When the fix ends, the mortgage moves automatically onto the lender's standard variable rate unless you have arranged a new product first. SVRs at the major BTL lenders currently sit between 6% and 7.5%.

Here is a worked example. Take a £120,000 interest-only mortgage, a common size for a two or three bedroom flat in Glasgow, Dundee or Aberdeen. On a 4.49% two-year fix, the interest costs £5,388 a year. On a 6.49% SVR, the same mortgage costs £7,788.

That is £2,400 a year, or £200 a month, for doing nothing other than missing a remortgage window.

Across a five-unit portfolio, the same slip can easily cost £10,000 to £12,000 a year. That money comes straight out of your profit whether you are watching it or not.

2. Your interest cover ratio at the stress rate

BTL lenders want your rent to cover the mortgage interest with room to spare. The usual requirement is 125% to 145% of the interest, tested not at your current rate but at a stress rate, typically 5.5% or higher. That is your interest cover ratio, or ICR.

On the same £120,000 mortgage, monthly interest at 5.5% is £550. At a 125% requirement, your rent needs to be at least £688 a month. At 145%, it needs to be £798.

A property renting at £750 a month in central Glasgow clears the first bar and misses the second. That does not make it a bad property. It means fewer lenders will offer you a product when you come to refinance, so your options narrow before you have even started looking.

Knowing where every property stands at the stress rate, before you speak to a broker, is the difference between a routine remortgage and a scramble.

3. Your lender concentration

If four of your five mortgages sit with the same lender, one change of policy affects most of your borrowing at once.

BTL lenders adjust their criteria regularly. Maximum property counts, LTV limits, portfolio landlord rules. A lender that was competing hard for your business last year may have quietly tightened this year. If most of your borrowing sits there, your refinancing options shrink exactly when you need them most.

With five or more mortgaged units, it is generally worth spreading your borrowing across at least two or three lenders, even if that means paying slightly more on one product for the flexibility.

The hard part is keeping them current

None of these numbers is hard to work out on its own. The hard part is keeping them current across every property and every mortgage, so the answer is there when you need it rather than rebuilt from a spreadsheet under time pressure.

That is where Lar comes in. It is being built to keep track of your fixed-rate expiry dates, your interest cover at the stress rate and your lender concentration, and to tell you when one of them needs your attention.

These numbers are illustrative and rates move; your broker will test them against your specific circumstances. This guide is general information, not financial advice.