quick question: I'm new to paying estimated taxes and I somehow forgot to file my last estimated taxes by Jan 15th this year - the payment due was for Sept-Dec 2018. I just realized this, and I want to pay it immediately to avoid accruing more penalties. I went to the IRS Direct Pay website and cannot select 2018 for 1040-ES filing/payment, only 2019.
My current plan is to mail the 4th Voucher for 2018 1040-ES with a check for the full amount I owe but I would definitely prefer to pay online. Can I submit the payment under 2019 online?