BM Solutions will apply a 5.25% stress rate on 5-year fixes from Monday next week.
Previously the lender applied the Prudential Regulation Authority’s 5.5% stress test on all buy-to-let mortgages.
Phil Rickards, head of BM Solutions, said: “The new stress rate forms part of our wider phased plans to support brokers in writing quality business in the new regulatory landscape.
“We created the rental income calculator in November to help higher and top rate taxpayers get the right level of cover for their individual circumstances, and then moved stress rates at the end of 2016.
“We are continuing to invest in our service and commitment to the intermediary market and plans for the next phase are underway.”
The new stress rate will not apply to further advances and porting applications will also be excluded.