How much would buying out my contract cost?

My dad is considering buying out my phone contract and getting me a new one at christmas but he isn't sure how much it will cost. I currently have an iphone5 and paying 37 pounds a month for it and it has 11 months left on the contract. He is wanting to get me an iphone5s. How much will it cost to buy out the contract?

That would depend on the carrier, and what their policy is on ending contracts early.