Bob Hill:The impound amount should be 14 minus the number of payments before the bill is due. This accounts for the 2 month cushion that the banks are allowed to have.
This is the calculation if the bill is paid 1 time per year. If it is paid 2x per year, make it 8 instead of 14 (2 month cushion plus the 6 months the payment covers). If taxes are collected 4x per year, then it would be 5. Subtract the number of payments before the bill is due, but don't count the payment made in the same month that the bill is due. For example, if taxes are due in October, you count the September payment but not October's payment.