Making an overpayment does not reduce the interest rate charged.
This question comes up in a variety of ways and the threads often go off topic with irrelevant calculations. The interest charged each year is exactly the same - we will return to this. Reducing the repayment is simply reducing the payment you are contractually obliged to make under your...
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If you your overpayments are enough to bring you into a lower LTV band, then you could apply for the lower rate applicable to that band.
Brendan