the figures are correct as ive checked online calculators but im still a bit bamboozled repayment mortgage at 4.390% =�550.47 but at 6.5% = �666.90 so how come 6.5% matches the monthly payment (�666.90) but 4.390% is way off by �100 more- surely 4.390% should be around �450? have i missed out anything or failed to take factors into account?
You're forgetting the capital repayment bit of the loan. The repayment mortgage pays off the interest and the capital over the period of the loan, so with a lower rate of interest the capital repayment bit represents a greater % of the monthly payment, so its probably correct. If you want us to check the figures for you, we also need to know the length of the loan period (see Dzug's response above).