Self Assessment Tax Calculator in the UK is an online tool that allows individuals who are self-employed or have other sources of taxable income to calculate their estimated tax liability for the current financial year. This calculator takes into account the individual's income and allowable expenses, and based on the latest tax rates and thresholds, calculates an estimate of the amount of tax owed to HM Revenue and Customs (HMRC). The calculation is for reference only, and it is important to note that actual tax liability may differ from the estimate provided by the calculator.