The lender has taken rates down to 3.55 per cent variable, from 4.25 per cent variable, on mortgages with a loan to value (LTV) of up to 60 per cent.
Rates have dropped to 3.95 per cent variable, from 4.75 per cent variable, on mortgages with an LTV of up to 70 per cent.
The calculation used to stress test the mortgage payment for such products to reflect the tax status of the main applicant has also changed.
The society will consider income from Airbnb lettings, and will also accept projected income and will consider unusual properties on both buy-to-let and holiday let cases.
Swansea said it has received a big increase in enquiries for holiday let mortgages in recent months, which appears to be a response to ongoing restrictions on overseas travel due to the coronavirus.
Swansea Building Society’s four branches and head office have remained open during the coronavirus crisis, while following guidelines around social distancing.
Alun Williams, chief executive of Swansea Building Society, said: “We are proud that we have remained open for both our savings and mortgage customers through the crisis, supporting our members in every way we can.
“As lockdown now eases, we are seeing an uptake in enquiry levels especially around the more specialist mortgage areas such as holiday let and self-build and we are delighted to be able to lower our rates on buy-to-let and holiday let mortgages in particular.”