The Surplus over Minimum Balance is the amount you have in your bank account above what you require to ensure that at no point over the next 12 months your account will be in debit.
Where this balance shows a Dr, this is the amount your account is short to ensure that at no point over the next 12 months your account will be in debit. Check your Projected Bank Balance column to see when this minimum balance will be reached.
It is important to note that these figures are projected assuming your payments in and bills paid out are for the values in your cashflow.