I received a letter from the IRS for my 2017 return, and I owe $3,169 from unreported 1099 and schedule D gain from a Vanguard fund I owned.

[chippymeow]

Why didn't Turbotax catch this?

[VolvoGirl]

Did you enter the 1099?     Tiubo Tax has no way of knowing or checking that you entered something wrong or in the wrong place or entered something twice  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.  They only Guarantee that the calculations are right based on the entries you made.

https://ttlc.intuit.com/community/charges-and-fees/help/what-is-the-turbotax-100-accurate-calculatio...

[Critter]

(what the letters from the IRS mean)

I GOT A LETTER FROM THE IRS   

https://ttlc.intuit.com/questions/3605673-i-got-a-letter-or-notice-from-the-irs

I AM BEING AUDITED

If you purchased Audit Defense:

https://ttlc.intuit.com/questions/2924451-i-bought-max-or-audit-defense-and-now-i-m-being-audited

AUDIT SUPPORT

https://support.turbotax.intuit.com/irs-notice/audit-support/