Understanding new LTV when porting

Mrs_Rachel_Trelfa

I was wondering if someone could, in layman's (lay women's) terms explain how the LTV/interest rate is worked out on the additional amount of borrowing when porting a mortgage?

We are moving house and the one we are purchasing is £318,000. Thanks to overpaying we only have just under £49,000 outstanding on our current mortgage but we are in a fixed period with ERC. So we want to port this over and borrow the additional £169,000 *gulp *. What I can't figure out is how the LTV and relative interest rate is worked out on that section. The reason being because we've seen a 10 year fix that we are potentially interested in but to get that we would have to repay our current mortgage and ERC so trying to work out if that would be cheaper or porting over and borrowing additional.

I hope my ramblings have made sense. And thanks in advance. 

[Deleted User]

Your existing £49k will transfer over with whatever the current interest rate and remaining product term. 

The extra £169k rates will be on a ltv based on (total borrowing (existing plus extra)) /  (purchase price) x100

Mrs_Rachel_Trelfa

Thank you so much for explaining.