Calderwood was born in Belfast on 26 December 1968 the elder of two daughters of Lesley and James Calderwood. Her mother is a psychiatrist and her father is an orthopaedic surgeon.She attended school at Methodist College, Belfast, and studied for a BA at Newnham College, Cambridge, graduating in 1990. She went on to take her medical degree at the University of Glasgow, graduating in 1993.Calderwood has a Lily and a daughter and one son.