If you oversubscribe an ISA by contributing more than the annual limit (£20,000 for 2026/27), HMRC treats it as an administrative error rather than a criminal offense [1][2][3]. You should contact your ISA provider or HMRC immediately rather than attempting to withdraw excess funds yourself, as this can complicate the repair process [1][2]. HMRC will instruct your provider to remove the excess contributions and any investment growth or interest earned on that overpaid portion [1][2][3]. You will then be required to pay income tax or capital gains tax on the earnings generated by the excess amount [1][2]. The ISA remains valid for your eligible contributions; the tax benefits are simply stripped from the oversubscribed portion [1][3]. For Lifetime ISAs, any government bonus paid on the invalid excess must be returned to HMRC [3].