Old Mar 17, 15, 12:17 pm
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Join Date: Aug 2010
Location: DCA
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Posts: 50,070
Presuming standard domestic change/cancel fee of $200:

(Value of old ticket) +$200 in new money - cost of new ticket = debit/credit due.

As others note, the fact that you pay the fee in new money rather than as a reduction of the credit only matters when the value of the old ticket < new.
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