DCO9753

My parents bought a house that they owned jointly. When my father died, my mother inherited his share. She has now sold the house. Because she has been in a care home for more than three years, there will be CGT to pay, but how do I calculate the amount? I could do one calculation for the 50% that she has always owned, and a second calculation for the 50% that she inherited more recently? Sorry if the answer is obvious, but I couldn't find it