My return was accepted and was a positive return amount. Now 5 weeks later the IRS sent me a letter saying there is a 1040 mistake and that I owe almost $2000.

[SweetieJean]

What did the IRS change that generated that result?

[brunectd]

they only stated that the tax due amount was wrong

[SweetieJean]

Call the number on the letter, and ask for a further explanation. The IRS does not notify TT.

[Lisa995]

It has to say more than "the tax due amount is wrong".  It should show some kind of figures on it....pull out the printed copy of your return that you kept for your records, can you tell where the discrepancy is?

[Critter]

And be aware that the IRS has been wrong a lot this year.

[VolvoGirl]

I would check over your return and see if you can see anything wrong especially in the payments section 1040 Schedule 5.  Make sure you agree with all the amounts listed.   Like is the difference the same or close to the refund you got last year?  Maybe you put down that you applied last year's refund to this year?  Or you put down you made a payment with an extension or paid an estimated payment that you didn't make?

A common error is showing an estimated payment 1040 schedule 5 line 66 you didn't make or payment with an extension (line 71) you didn't send in.  Sometimes people start an extension form on purpose or accidentally and an amount gets entered for a tax due to send in with the extension.

Or you claimed Excess Social Security paid on line 72.  That happens when you are married and enter both spouse's W2s under the same name.

[Critter]

FYI... the return was accepted for PROCESSING ... and during processing something was found ... are they correct ? 

See this TurboTax support FAQ for an IRS letter - https://ttlc.intuit.com/questions/3605673-i-got-a-letter-or-notice-from-the-irs