How to calculate DateFormula field


I want to calculate “Production date” and don’t know how to calculate this two fields:
"Item Ledger Entry". “Expiration date” is DATE field.

Item.“Expiration Calculation” is DateFormula field.

I try this formula:
“Production date”:= “Item Ledger Entry”.“Expiration Date” - CALCDATE(STRSUBSTNO(’<CW-%1>’,Item. “Expiration Calculation”), “Item Ledger Entry”.“Expiration Date”);

But this formula didn’t work :frowning: Maybe you can help find problem?