The lender is increasing the maximum number of let properties for landlords to hold on completion from seven to 10.
And for remortgages, Santander has reduced the maximum number of mortgaged let properties from five to three.
The bank offers free standard valuation up to a property value of £2.5m available on all products, either standard legal fees paid or £250 cashback for buy to let remortgages.
The lender would not elaborate on its changes on residential affordability rates.
A spokesperson from Santander told Mortgage Solutions said: “We work to support all customers secure the right mortgage to meet their needs, providing market leading products and services.
“As a prudent lender, we continually review our offering in line with the market and have recently made some changes to our affordability calculator.”