Assuming your other date is stored in TheOtherDate, you can use:
Dte_1 = DateSerial(Year(TheOtherDate), Month(TheOtherDate) + 1, 0)

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Doug Steele, Microsoft Access MVP
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>I have a field that contains a date (say Dte_1) I would like to
> introduce a calculated field that would give the date of the last day
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>
> Can anybody help with a formula please.