Turbo Tax is a self prepared return. They only guarantee the calculations are right based on your entries. They won't know if you entered something wrong or twice or in the wrong place or left something out. It doesn't check against any outside sources. The IRS has copies of all the W2s and 1099s your employer and banks/brokers, etc. sent in to match against. Turbo Tax only checks the calculations of what you entered. It is your responsibility to check it over before you file.