I am aware of no case documented on this forum where either 2018 or 2019 TurboTax incorrectly calculated the taxable amount of Social Security benefits. Given the millions of tax returns prepared using TurboTax that include taxable Social Security benefits and the fact that the calculation method has not changed for many years, it's extremely unlikely that TurboTax makes any such calculation error.
The most common cause of a discrepancy between the amount of taxable Social Security benefits determined by TurboTax and the by the IRS is that the user made an error on their tax return that resulted in an incorrect amount of other income being reported and the IRS corrected that, causing a change to the taxable amount of Social Security benefits. Within a certain range, the taxable amount of Social Security benefits depends on the amount of other income on the tax return.
