You know the part that slows down a buy to let mortgage application, it is rarely the rate you picked. A buy to let mortgage is a loan for a property you plan to rent out to tenants rather than live in yourself. Consumer buy-to-let: A buy-to-let mortgage that is not taken out mainly for business purposes, and it can fall under a different regulatory framework. Deposit size and loan-to-value ratioA 25% deposit is still the most common starting point for a buy to let mortgage. What documents do lenders want to see for a buy to let mortgage loan?