You must specify to the bank that extra money should be applied as a principal only payment. Otherwise they always have and always will apply the money as normal payment(s) made ahead of schedule. This is the default. Many people will send payments early if traveling or going out of the country. Then they can skip paying while they are away. If the bank applied this money as principal only then these people will be in default. This is not a bad business practice, but actually the way extra loan payments work and have always worked. If you do not specify principal only, then it won't be applied to principal only.