Indiana calculates the underpayment penalty on a quarterly basis. Even if all four estimated payments were made on time, each installment must be large enough to meet the required amount. This is 25% of 90% of the current-year tax. Or 100% of the prior-year tax).
If earlier quarterly payments were insufficient, a small penalty may apply for those quarters, even if you ultimately overpaid.
When you change the 4th payment date to 2025, TurboTax reallocates that payment to earlier quarters, which removes the penalty but wouldn't reflect the actual payment timing.
If your 2025 income was uneven during the year, you may be able to reduce or eliminate the penalty by using Indiana’s annualized income method (Schedule IT-2210A).
Payment of Indiana Estimated Tax by Individuals.
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