"My deal stacked in 2021. Why won't the same numbers work now?"
If you bought a rental four or five years ago, you probably remember how easily the mortgage went through. The rent covered the payment with room to spare, and the lender barely blinked. Bring the same property, the same rent and the same deposit to a lender today and it can fall short by tens of thousands of pounds of borrowing. The property has not changed. The test the lender applies to it has.
That test is the buy-to-let stress test, and understanding it is the difference between a deal that stacks and one that gets declined.
What the stress test actually is
Lenders do not size a buy-to-let loan on the rate you actually pay. They size it on a higher, made-up rate to check the rent would still cover the mortgage if rates rose. Two levers do the work:
- The stress rate: an inflated interest rate the lender tests against.
- The interest cover ratio (ICR): how far the rent has to exceed the interest at that stressed rate.
Both come from the Prudential Regulation Authority's underwriting standards, set out in supervisory statement SS13/16 and in force since 1 January 2017 (Bank of England / PRA). They are the reason the maths tightened.
The stress rate
As a rough rule, the stress rate is the higher of:
- your pay rate plus 2 percentage points, or
- a floor of around 5.5%.
The PRA asks lenders to test at least a 2 percentage point rise, and to assume a minimum rate of about 5.5% where the fixed period is under five years. Five-year fixes are often exempt from both, which matters later.
The interest cover ratio
The ICR is the multiple of the stressed interest the rent must cover. Typical figures:
- 125% for basic-rate taxpayers and most limited-company borrowers.
- 145% for higher-rate taxpayers.
The higher band exists because a higher-rate landlord keeps less of the rent after tax (Section 24 restricts mortgage-interest relief to a 20% basic-rate credit for individuals), so the lender wants a bigger cushion.
Why 2021 deals passed and today's fail
Here is the flip that catches people out. The stress rate is a "higher of" calculation, so which part bites depends on where pay rates sit.
- In 2021, buy-to-let pay rates were around 2.5%. Pay rate plus 2% is 4.5%, which is below the 5.5% floor, so the floor decided the test. Almost everyone was stressed at roughly 5.5%.
- In 2026, at the time of writing, pay rates are around 5.5%. Now pay rate plus 2% is about 7.5%, well above the floor, so the +2% rule decides the test.
So the stress rate quietly climbed from about 5.5% to about 7.5% on the same property, and a higher stress rate means the rent supports a smaller loan.
A worked example you can reuse
Take a flat let at £1,000 a month, or £12,000 a year, held by a higher-rate taxpayer (ICR 145%). The maximum loan a lender will offer is:
Max loan = annual rent / (ICR × stress rate)
| Year | Pay rate (approx) | Stress rate applied | ICR | Max loan on £12,000 rent |
|---|---|---|---|---|
| 2021 | 2.5% | 5.5% (the floor bites) | 145% | £150,470 |
| 2026 | 5.5% | 7.5% (pay rate + 2% bites) | 145% | £110,345 |
Same rent, same flat, same landlord. The borrowing power falls from about £150,000 to about £110,000, a drop of roughly 27%, purely because the stress rate moved. If you were banking on a 75% loan against a £200,000 value (£150,000), the 2021 version cleared it and the 2026 version leaves a £40,000 hole you now have to fill with cash.
How landlords are getting deals to stack again
The test is fixed, but several of its inputs are not:
- Use a five-year fixed rate. Because five-year fixes are usually exempt from the +2% and the 5.5% floor, many lenders stress them at or near the pay rate. That single choice can restore most of the lost borrowing.
- Put down a bigger deposit. Dropping from 75% to 65% loan-to-value lowers the loan you need the rent to support, and often comes with a lower pay rate too.
- Hold in a limited company. Company lending is typically assessed at 125% ICR rather than 145%, which is a meaningful uplift for a higher-rate landlord. Weigh it against running costs and take advice first.
- Top-slicing. Some lenders let you use surplus personal income to bridge a rental shortfall.
- Chase yield, not price. A higher rent relative to price is the only input that helps every version of the test at once.
Run your own numbers
Before you offer on anything, work out the maximum loan the rent will actually support at today's stress rate, not the rate you hope to pay. Our buy-to-let mortgage stress test calculator does the ICR maths for you, so you can see in seconds whether a deal clears at 125% or 145% and where the borrowing caps out.
The bottom line
Nothing is wrong with your old deals. The stress test simply moved from a 5.5% world to a 7.5% one, and on the same rent that shifts borrowing power by a quarter or more. Size every purchase on the stressed rate, treat the pay rate as a bonus, and lean on five-year fixes, lower LTVs or company structures where the numbers are tight.
This is general information, not tax or financial advice. Check current rates and lender criteria, and speak to a broker before you commit.
