How to calculate balance when the date change

[jackson_hollon]

I need to calculate the balance based on the date change (G1). If the end date (column B) or the termination date (column C)is less than the last end month (N1), the balance should be zero, otherwise, it should show on column O the balance of the amount (column F less all the amount was used)

I need the formula be able to calculate the balance when the beginning date change (column G).

Thank you for the help.