The Pirates of the Caribbean actress, who is currently appearing in The Children's Hour in London's West End, insisted that fame hasn't changed her as a person.
The 26-year-old star was brought up in Teddington, London, with her mum Sharman MacDonald and dad Will Knightley.
Keira told The Mirror: "I was always brought up by Mum to treat people how I wanted to be treated myself. Just because I have had some success that does not change anything.
"From the age of 7 my goal was to buy my own flat. I even had a jar when I was growing up full of pennies which I had saved.
"I was able to buy a flat aged 20 and become financially independent. It made me feel good to have my own roof over my head."
Keira is reportedly dating Klaxons frontman Jamie Righton.