Since you will not meet the testing period, if you use the last-month rule you'll pay a 10% extra tax on the amount you contribute over what you are eligible to contribute without using the last-month rule. Because you will be covered for only two months, the amount that can contributed on your behalf by you or your employer without using the last-month rule is 2/12 of the annual limit.
Because you will be covered for December, TurboTax will automatically calculate the maximum contribution based on the last-month rule. You can force TurboTax to calculate your maximum contribution without using the last-month rule by indicating that your coverage is for October and November instead of November and December. The details of which months you are covered will not appear on your filed From 8889.
