Can you mail tax return and check for amount due in same envelope?

Yes, you can mail the return with the payment in one envelop.

If you choose to mail your tax payment:

• Make your check, money order or cashier's check payable to U.S. Treasury.
• Enter the amount using all numbers ($###.##).
• Do not use staples or paper clips to affix your payment to your voucher or return.
• Make sure your check or money order includes the following information:
• Your name and address
• Daytime phone number
• Social Security number (the SSN shown first if it's a joint return) or employer identification number
• Tax year
• Related tax form or notice number

You can look up the address to mail the return and payment here:  IRS Where to File Paper Tax Returns With or Without a Payment

When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS received the return.