I owe the federal government, is there a due date that I need to pay them by?

[VolvoGirl]

If it's for your 2018 tax return the due date was April 15, 2019.  You can pay anything directly at https://www.irs.gov/payments 

[Anonymous]

the payment due date is the same as the return due date 

right now your looking at a 5% late payment penalty on what you owe.  on May 16th it will be 10% 

if this is your first time paying late, you may be able to request abatement of penalty,