The IRS web site won't show how much tax you owe until after they finish processing your tax return. You should pay the amount due that was shown on your tax return now. You don't have to wait until the IRS web site shows that you owe it. The deadline for paying is long past. It was April 18.
Ideally the IRS web site should never show that you owe tax. You pay when you file your tax return, or earlier, and they apply the payment when they process your return.
