I have a textbox on the form that displays the last invoice number used named
“LastInvoice” and it has a control source of:

=DMax("[InvoiceNumber]","tblLog")

The "InoviceNumber" is in the format "0000-yy"

Is there a way to code the Default Value of the textbox “InvoiceID” so that
it's the “LastInvoice” textbox value, but increases it’s “0000” value +1.

So now the Default Value of textbox “InvoiceID” is the “LastInvoice” textbox
value “0000” +1 & “-“ & Right([Date],2)

Thanks

You could use a recordset rather than DMax, but there's no need to do that.

The important thing, though, is that you follow Ken's advice and split your
existing field into two separate fields, and concatenate the fields into a
single value for display purposes in a query.

Have two separate pieces of information in a single field, such as you
currently have, is actually a violation of database normalization
principles. You've already seen one of the effects of doing that: it's
difficult to work with the data!

BTW, simply reposting your question again in the same thread is NOT going to
get you a different answer. If you need more information about the answer,
or realized that you didn't give us all the details originally, indicate
what's different the second time: don't just repost the same question!