Reg. § 301.6403-1 Overpayment of installment.

If any installment of tax is overpaid, the overpayment shall first be applied against any outstanding installments of such tax. If the overpayment exceeds the correct amount of tax due, the overpayment shall be credited or refunded as provided in section 6402 and §§ 301.6402-1 to 301.6402-4, inclusive.