The IRS is stating that you have a balance due on your tax return that was filed. Did you fail to report income or enter income incorrectly on the tax return? The IRS notice should tell you exactly what the IRS added, changed or deleted from the filed return to arrive at the balance owed.
See this IRS website for a CP501 notice - https://www.irs.gov/individuals/understanding-your-cp501-notice
Use the TurboTax Audit Support Center to assist you with understanding the notice you received from the IRS - https://support.turbotax.intuit.com/irs-notice/audit-support/
The TurboTax 100% Accurate Calculation Guarantee is for any calculation errors caused by the TurboTax program. It does not cover any user errors or errors of omission. TurboTax will reimburse you for any penalties and interest owed and paid for by the user of the software based on a program calculation error.
See this TurboTax support FAQ - https://ttlc.intuit.com/community/charges-and-fees/help/what-is-the-turbotax-100-accurate-calculatio...
