Calculating a reimbursement amount in a subform

[TerriD]

New to Access Form Design and thanking you in advance. Trying to create a form that will display the amount that is owed to an employee.

Our office gives its employees a $125 supply allowance each year. When an employee submits a receipt for a partial amount (say they spend only $35), I enter the amount in the PurchaseAmount field of my subform. The ReimbursementField control source is =IIf([PurchaseAmount]>=125,125,[PurchaseAmount]). The correct amount of $35 is displayed.
(There is no beginning balance or ending balance field on the form.)

When a subsequent purchase amount is entered and is over the amount of the remaining balance, (let's say spent $100 and only has $90 remaining) how can I have the form display the correct amount of $90? The closest answers I came across suggested using recordset clone in an AfterUpdate event, but I just can't figure out the proper way to write the calculation. My main form name is "Supply Purchases"; subform name is "Supply Purchases Subform. Thank you again.

[aytee111]

Use the Remaining Amount in you calculation:
if purchase amount > remaining amount, remaining amount, purchase amount
Put totals somewhere on the form - Sum(PurchaseAmount), also one for remaining amount if there aren't these already

[TerriD]

Thank you for the answer. I"m stuck on how to tell Access to start with $125, yet only use it once, as a Beginning Amount. I calculated the "RemainingAmount" as [BeginningAmt]-[PurchaseAmt]. But each subsequent purchase subtracts from $125. Thank you for any suggestions I can try.

[aytee111]

BeginningAmt - Sum(PurchaseAmt)

This needs to be on the header or footer of the subform as it needs to get a total of all the Purchase Amts entered up to now

[TerriD]

Perfect! Thank you very much