doesn't matter. you will be subject to underestimation of taxes but by making payment and filing for an extension you will avoid late filing and late payment penalties which can are 5% a month for up to 5 months. if you mail post mark must be on or before 4/18 and you may want to use a tracking service.
unless you end up with an overpayment you need to file an extension otherwise you not only will be subject to estimated tax penalties but also late filing penalties. the safest thing to do is to go online to IRS website and use Direct Pay to make payment and at same time get an extension reason for payment - extension
https://directpay.irs.gov/directpay/payment?execution=e1s1
do this ASAP you can actually schedule withdrawal for 4/18 so if issues occur you have the option of mailing (postmark must be by midnight on 4/18)
