Can a payor use an accidental overpayment of support to offset arrears they owe later?

An accidental overpayment isn't automatically lost, but it also isn't something a payor can simply apply against future arrears on their own say-so. Generally, if a genuine overpayment can be established, for example through payment records showing more was paid than was actually owed for a given period, this is something that can be raised with the Family Responsibility Office or, if necessary, the court, as part of sorting out the accurate running balance between what was owed and what was actually paid.

The key practical point is that a payor shouldn't unilaterally decide an overpayment exists and then simply reduce or stop future payments to "even things out," since this can itself look like a new default and trigger enforcement action, regardless of the payor's good intentions. Instead, the overpayment needs to be documented and raised properly, so that FRO's or the court's records accurately reflect the true balance owing going forward. A payor who believes they've overpaid should raise it promptly with FRO, with supporting payment records, and get legal advice if the amount is significant or the issue isn't resolved quickly.