TMW, part of the Nationwide Group, will leave its existing stress rates unchanged, while the move will not impact fixed-rate mortgages over five years.
The specialist lender will still use the higher of either the stressed rate or product rate against a rental cover of 125%.
TMW said the move will strengthen landlords’ ability to withstand future Bank of England base rate rises.
Henry Jordan, managing director of TMW, said: “As a responsible lender, we continually review our criteria and these changes are intended to give an extra measure of protection to our customers.
“Tiering stressed rates by LTV ensures alignment to our pricing structure and reflects the likely options available to landlords when their existing product matures.
“Maintaining a stressed rate of 4.99% on 5-year fixed rates recognises the additional payment security that longer-term products provide.
“Together, these changes strike the right balance between prudence and supporting the market.”
Intermediaries cam submit applications on existing terms until 8pm on 19 November 2014.