Borrowers monthly payments to their lender repay the interest on the mortgage, these payments do not reduce the total amount borrowed or the capital. The full amount of the mortgage will need to be repaid to the lender at the end of the agreed mortgage term. This term is clearly stated in your mortgage offer and may be up to 25 years.
Borrowers may be advised to have an 'investment vehicle' in place to ensure that the outstanding capital balance at the end of the mortgage terms can be repaid. This however, can not always be guaranteed to be sufficient to repay a mortgage.