Yes, they are optional to pay. They don’t get sent with your return so the IRS won’t be expecting them. You can change the amount and pay what you want. You can pay directly on the IRS website https://www.irs.gov/payments
Be sure to pick the right kind of payment and year.....2025Estimate
If you want to adjust them or print new ones,
You can just type W4 in the search box at the top of your return , click on Find. Then Click on Jump To and it will take you to the estimated tax payments section. Say no to changing your W-4 and the next screen will start the estimated taxes section.
Or Go to….
Federal Taxes or Personal (Deskop H&B)
Other Tax Situations
Other Tax Forms
Form W-4 and Estimated Taxes - Click the Start or Update button
The underpayment penalty will be assessed if any of these apply:
"If you don’t pay enough tax through withholding and estimated tax payments, you may have to pay a penalty."
"You also may have to pay a penalty if your estimated tax payments are late, even if you are due a refund when you file your tax return."
To avoid the under payment penalty:
The amount you owe is less than $1,000, after subtracting withholding and refundable credits.
You paid 90% of the tax that you owed for the current year.
You paid 100% of the previous year tax, (110% for higher incomes).
If your previous year's adjusted gross income was more than $150,000 you will have to pay in 110% of your previous year's taxes to satisfy the "safe-harbor" requirement.
"Typically, underpayment penalties are 5% of the underpaid amount, and they're capped at 25%.
Underpaid taxes also accrue interest at a rate that the IRS sets annually."
To avoid this situation it is recommended that you adjust your W-4 with your employer or pay estimated taxes.