I haven’t filed yet, but received a Form 1040-V in the mail from the IRS. Why? I’m not sure if I owe tax or not because I haven’t input all of my deductions yet.

[AnthonyC]

Was it attached to a notice from a prior year - i.e. you owe taxes from a prior year?  Or was it just a blank 2017 Form 1040-V?

It would be unusual for the IRS to preemptively send you a Form 1040-V.  The only scenario I could see where the IRS may send you one is if you have owed taxes in the past and/or if you were late on a payment.  

Here is a link to the official Form 1040-V from the IRS.  Note what the form looks like and also the addresses listed on the second page to where you are supposed to send the Form.  Since this is unusual, it could potentially be a scam, so compare it to what you see here -

https://www.irs.gov/pub/irs-pdf/f1040v.pdf

Regardless, I would not use that form that was sent to you (unless it accompanied an official IRS notice from past due taxes).  TurboTax will print up a Form 1040-V for you if you owed taxes and you can always make a payment directly on the IRS website.

Edit:  See VolvoGirl's answer below - it may not be as unusual as I originally thought.  But, I would still recommend checking the addresses to ensure its legitimate and/or just using the voucher TurboTax produces or using the IRS direct pay website if you do owe taxes. 

[Edited 3.30.18 at 11:18am EST]

[VolvoGirl]

I always have refunds but get a blank 1040V and 1040ES forms every year from the IRS.  You don't have to use them.  If you paid estimates the year before they will send you blank ones.  In fact I gave up printing the estimates from Turbo Tax and just write the amount the IRS ones.