Corporation tax is a tax on the taxable profit of a limited company. Taxable profit is different from accounting profit. For small companies, the corporation tax rate is 20% on the taxable profit. Normally, a limited company does not have to pay any other taxes than corporation tax.
Small companies have to pay their corporation tax liability by 9 months and 1 day after the year-end to HM Revenue and Customs (HMRC). They also have to submit Corporation Tax Return (CT600) by 12 months after the year-end. If you do not pay the tax liability in time or submit CT600 in time, there are penalties and interest in addition to corporation tax liability.