How can I file for an extension if I have no W2 to determine my estimated taxes owed ??

[BillM223]

You will have to make a best-guess when you file the extension.

The IRS just wants to know how much you are paying. You can put any amount there, and the extension will work.

The problem for you is that if you underestimate how much tax you will owe (and therefore don't pay enough with the extension), you will be charged interest starting on July 16th.

So you are motivated to file the extension and then get that W-2 or its information as quickly as possible, in order to file the correct return. Note, I am sure you know this, but because the extension is good until October 15th, you can file your return any time before that to cut off the interest.

[fanfare]

You don’t need to file Form 4868 if you make a payment using the IRS
electronic payment options. 
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You can pay all or any part of your estimated income tax due and **indicate that the payment is for an extension** using Direct Pay, the Electronic Federal Tax Payment System, or using a credit or debit card. Your extension is then automatically granted and you will receive a confirmation number for your records.

Any amount, even $10 will do the trick.

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If you e-file Form 4868 and mail a check or money order to
the IRS for payment, use a completed paper Form 4868 as a
voucher. Please note with your payment that your extension request
was originally filed electronically.

[Anonymous]

your employer was supposed to file copies of the W-2 with the Social Security Adm back in Feb or earlier. The SSA transfers the federal data to the IRS and the state data to the states. 

if the employer has transmitted the info to the SSA, you can get a transcript of the federal data from the IRS, for state data you would need a copy from the SSA.  

are you sure that your "employer" treated you as an employee rather than as an Independent Contractor (IC)?  if not, then they should have sent you a 1099-misc.  this too would be available in IRS transcript.

https://www.irs.gov/site-index-search?search=transcript&field_pup_historical_1=1&field_pup_historica...

it's important to determine employee/ IC status. if an IC you'll owe self-employment taxes in addition to income taxes.   as an employee, you would see medicare and social security taxes deducted from your paychecks.  

if an employee you can use form 4852 as a substitute for the W-2.  your employer will be contacted.