The five-year discount deal at 3.45 per cent and 50% loan to value (LTV) is available to applicants over 60.
There is no maximum age but borrowers must be retired and receiving their pension.
Newbury will offer a free standard valuation for properties up to £1m, as well as free legals for remortgages and accept over payments.
It comes after the society increased its age limit for mortgage lending to 90.
Existing borrowers of Newbury Building Society can also transfer onto the product to borrow additional funds.
Roger Knight, lending manager at Newbury Building Society, said: “As a mutual, we listened to our members who expressed a need for a RIO mortgage.
“People are living for longer and therefore, as a lender, it is our responsibility to ensure we are offering the right products at the right time.
“We hope our RIO five-year discount variable mortgage product ticks all the correct boxes and enables borrowers to fulfill their retirement ambition.”