I claimed 8 allowances on my w4, im single with 2 kids 1 job. I just noticed no fed.taxes were are being taken out, will i owe the irs?

I made about 19,000 so far this year..

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Assuming you can claim Head of Household with two children, your standard deduction would be $9,250 and 3 exemption at $4,000 each would be $12,000.  So nothing would be taxed under the total of $21,250.   Also you might qualify for a $2,000 child tax credit for the two children.   You probably qualify for an EIC (Earned Income Credit) to boot.  So zero withholding seems appropriate.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**

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Use the TurboTax calculator TaxCaster to get an estimate of taxes owed or a refund - https://turbotax.intuit.com/tax-tools/calculators/taxcaster/