resolving repeating entries in sub form

[cvgope]

I am having a database for "Orders & Payments". There is a Main Form called "frm OrdersandPayments" for entering all the Payments info of various customers/suppliers. Also, there are 5 Nos. Subforms created for entering stage wise Payments made i.e., Advance, 1st, 2nd, 3rd and Final State in the Main Form.

There are Deductions based on Bill Value i.e., Tax Deduction (TDS), Work Contract Tax (WCT) and 5% Deductions. Net Amount Payable is arrived by deducting (Using code) standard deductions(TDS, WCT, 5%) from the Bill Submitted Value on each Subform. The Advances Paid is carried forward from Advance to Final Stage Payments and these are also deducted from the Bill Submitted Value. All these calculations are working fine.

Coming to Final Stage Payment Subform: Assuming that the Party/Supplier has submitted Final Bill for Rs.500000/-. Since the Final Inspection of the Work is to be carried out to take the Final Measurements, the same bill value has to be considered as "3rd Stage Bill" instead of "Final Stage Bill".

The taxes (TDS, WCT & 5%) to be deducted will be on Rs.500000/- and the remaining Balance has to be paid to the Supplier less Advances Paid so far also. Upto this this is working fine.

After releasing the 3rd Stage Bill Payment and after a few days, assuming that the Final Inspection was done and it is certified that the Party has done work for Rs.550000/- and the same has to be taken into account for releasing payments.

But when entering the Bill Value of Rs.550000/- in the "Final Stage Subform", the Taxes to be deducted on the Remaining Rs.50000/- but not on entire bill value of Rs.550000/- (assuming that we have already deducted taxes for Rs.500000/-).

Pls. see the Last Record in the "frm OrdersandPayments" attached herewith and help me out of this as I am new to access