Forgotten how to understand a statement lol?

After being on a DMP for so many years i have forgotten how they add the interest on each statement.

I have a balance and the statement says estimated interest will be £7.23.

Payment due by 28th May

They have added interest each month, for the past 6.5 yrs. so i never really take much notice.

I am going to pay the full amount off this month before the 28th of May, does this mean any of that estimated £7.23 interest will be added.

Or is the balance as it stands 100% all i owe till the 28th?

Sounds so dull, but been so long since i paid full attention to how and when they add interest.