In the tax law of the United Kingdom, tax credit overpayment occurs when a claimant (person filing taxes) has received more Working Tax Credit (WTC) or Child Tax Credit (CTC) than HMRC’s final end of year calculations awards them. This can be caused by official or claimant error or neglect, or simply because the provisional payments were based on out of date information. This article is solely about overpayment, not about details of the tax system as a whole.