How much will I pay?

Darrenpk

Hello, 
My fixed term mortgage is coming to an end on the 3rd November 2020, when this happens I will be moved to the banks Follow on rate of 3.35%. Currently my mortgage balance is roughly £30K so I'm planning on staying with the Follow on rate as I hope to have paid it off within 2 years, as it stands I have roughly £10K in NS&I which I am planning on putting towards my mortgage, the thing is, I won't be putting the 10K towards my mortgage until roughly the middle of the month, say the 15th November. I'm wondering how the bank will calculate how much I will have to pay for November? Is the interest calculated at the start of the month or the end? Perhaps somewhere in between? Because up to the 15th November my mortgage balance will be £30K, after the 15th November it will be £20K, so will I be charged interest on £30K or £20K?
I hope that makes sense, I can't find anything that mentions this kind of senerio on Google

Many thanks 

D.L

Interest is calculated on a day-by-day basis so it will be somewhere in between. There isn't a cutoff point where you could make a large saving on interest paid.

MovingForwards

Why don't you see what 2 year fixed rates your lender has, rather than going onto their variable rate, make the maximum 10% (if that's what theirs is) overpayments and clear the mortgage at the end when no ERCs. That way you have your £10k as a fall back, unless you've got a lot more in the bank.