Why is the IRS billing me for a late payment when I paid before 4-15-24?

[psuereal]

The online Turbotax software said I could pay in 3 installments or before April 15th. I paid one payment in April for the whole amount. The IRS is acting like the suggested 3 monthly payments were late!

[VolvoGirl]

What 3 installments?  Were they the 1040ES payment slips?    THOSE ARE NOT FOR YOUR TAX DUE.

The 1040ES are estimates for next year. The 1040ES quarterly estimated tax payments DO NOT get sent to the IRS or state with your return. So they won't be expecting them.  They are optional to pay. Turbo Tax is very conservative and doesn't want you to owe too much next year. They might have printed out if you got a one time large income this year. Like if you took a IRA or 401K distribution. You can ignore them. You might want to adjust your withholding at work so you won't owe too much next year.

Your tax due is a Single 1040 V voucher unless you entered your bank account for the IRS to pull it out.

[VolvoGirl]

Or you have an underpayment penalty.  If you do not pay enough tax during the year, you may have to pay a penalty for underpayment of estimated tax. Even if you are getting a refund you can still owe a penalty for not paying in evenly during the year.  Generally, most taxpayers will avoid this penalty if they owe less than $1,000 in tax after subtracting their withholdings and credits, or if they paid at least 90% of the tax for the current year, or 100% of the tax shown on the return for the prior year, whichever is smaller. It is included in your tax due or reduces your refund.

Do you have a penalty on 1040 line 38?  It's not for filing or paying late.  It doesn't have to do with last year's tax return or not paying estimates for this year.  The penalty is an "estimated" amount.    It's a penalty if you owe too much or for not paying in enough withholding during the year or not paying in evenly.  Even if you are getting a refund you can still owe a penalty.  It's very common and normal and expected for the IRS or state to bill you for more or send you a refund.