Most lenders will expect that the rental income on the property will exceed the mortgage repayments. The level at which this becomes acceptable varies between lenders. Some lenders will consider the rental income, whereas others will only be interested in your standard income.
Fixed rate buy to let mortgages allow the borrower to pay a set rate for a fixed period, usually between two and ten years. The advantage of a fixed rate mortgage when buying to let is that you can calculate exactly what your future costs are going to be. It is certainly worth being aware of the penalties for early repayment that are included in some buy to let mortgages. Some mortgage lenders offer a flexible deal that allows you to overpay, underpay and even take payment holidays without any penalty fee being incurred. There are an enormous variety of different loans on the market, generally extending for between five and 45 years and between £15,000 and £1 million.
When looking for a buy to let mortgage deal it is worth looking at both the headline interest rate and the APR (Annual Percentage Rate), which should include all set up fees and administrative costs. You should be thinking about flexibility: does the loan allow early repayment and what will happen if you face a long void period. You should also be aware of the possibilities of remortgaging. It is common practise amongst landlords to free up capital by remortgaging and using the savings to help buy further properties.