As dasherman said, it seems that you have a fixed rate mortgage. The difference in your payments is not based on whether you have an interest only mortgage or a capital & interest mortgage. It depends on the type of rate you have (fixed, variable, tracker etc.). If there has been no reduction, it seems you are tied in to your fixed rate. When this period finishes, you are likely to benefit from a lower rate but you will need to confirm this with either your lender, your mortgage adviser or by checking your mortgage paperwork.