Say at the end of year 1 I have a cash ISA with annual interest maxed out at £15,000 (I'm not certain of the exact maximum)
For that year, suppose I am paid tax free interest at 2% so my balance is now £15,300. Suppose over year 2 I then pay in a further £15,000.
My total balance is £30,300. My question is - what "part" of this total cash will interest be calculated on.
For example, will I get 2% interest only on the £15,000 I paid in over year 2? Or will I get paid interest at 2% on the whole £30,300, but have to pay tax on £15,300 of the total cash pot?