You are allowed to have as many buy-to-let properties as you can afford, however, there may be a limit to the number of mortgages lenders are willing to provide. Major lenders usually have a cap in place, either by the number of BTLs or the borrowable amount - this helps them counter the risk they're taking by lending for your buy-to-let. Also, remember that the higher the number of properties you have, the fewer the lenders willing to deal with you. If you want to be a prolific BTL homeowner, you might want to work with a special buy-to-let broker.