It's simple maths ... There is no error .. Unless the company is...

It's simple maths ... There is no error .. Unless the company is wrong .. Any finance manager will tell you that the first monthly payment is 95% plus interest and a tiny bit of original debt repayment ..the opposite is true of the last month if repayment ... Simple .. However .. Because of the compound effect alluded to by Dom .. The original debt ( principal ) is not HALF paid off when HALF the repayments are made .. Many people are confused by this ... It is not a linear reduction .. To put it another way ... That's the last I am going to say on the subject .. It's more about their ability to grow .. Which is a bigger question