Several tax-preparation services, including TurboTax and H&R Block, allow users without accounts to calculate how much tax they owe and when it is due, according to the company websites. TurboTax also helps users determine whether they must pay estimated taxes.
H&R Block and TurboTax both have online tax calculators. A user enters information about his filing status, number of dependents, age, income and deductions, explains TurboTax. He also adds credits and prior payments. The calculators show the amount the user owes or can expect to have refunded. For taxpayers who must pay estimated taxes, TurboTax has a detailed list of questions that help determine the estimated tax payment requirements.