Ulster Bank Breakage Calculation Understanding

Hi

I am trying to get an understanding of how my bank calculates the mortgage breakage cost.

I am aware there is this super helpful thread:

However, I would love to be able to calculate the fee myself.

I have my mortgage with Ulster Bank. The break fee formula is:

Redeemed amount x (R - R1) x Time remaining in days until the end of the fixed rate period) divided by 360

My question specifically relates to “R”. The meaning of is:

R means the interest rate available to the lender for funds placed in the money market on the start date of the relevant fixed rate period for the duration of the relevant fixed rate period

Where can I see interests rates?

Thanks

@lexio7 Resurrecting this thread to say that in the following post you can see a worked example of estimating a break fee, including a link to interbank interest rates (which serve as a proxy for Ulster Bank's R and R1 rates):