さがく差額sagaku
1.

The remaining amount after deducting a specified quantity or value from another amount, often referring to financial transactions.

2.

The difference in value between two amounts, typically indicating a variation that requires calculation or adjustment.

3.

An amount that needs to be paid or received to settle a difference between two costs, often used in contexts such as insurance reimbursements or pricing discrepancies.

Example:

遅延便については、オリジナルの出発日に基づくシーズナリティを適用するため、マイル差額の払い戻しはいたしません。