What this line means
The portion of your overpayment on line 16 you want applied to next year’s estimated tax instead of refunded. This works the same as line 36 on Form 1040. Once you make this election on the amended return, you cannot reverse it — the IRS applies the credit to the following tax year’s estimated payments.
Does this apply to you?
Easy to overlook
The election is irrevocable once the amendment is processed If you direct part of the overpayment to estimated tax on line 18, you cannot later change your mind and request a refund for that portion. Consider whether you need the cash now or can afford to apply it to next year’s taxes before making this election. 1 IRS Form 1040-X Instructions — Line 18
The credit applies to the following tax year, not the current one If you are amending your 2024 return and have an overpayment, the estimated tax credit on line 18 applies to 2025 estimated taxes. If you are already past the 2025 tax year when the amendment processes, the credit applies to the year following the amended year. Timing matters for quarterly estimated payment calculations. 2 General filing pattern — timing of estimated tax credit application
Watch out for this
Applying the full overpayment to estimated tax when you need the refund for current expenses. The credit is not liquid — it reduces future estimated tax obligations but provides no cash now. Seniors on fixed income should generally take the refund unless they are certain the estimated tax credit is more beneficial.
Footnotes
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IRS Form 1040-X Instructions, Line 18. https://www.irs.gov/instructions/i1040x ↩
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IRS Form 1040-X Instructions, Overpayment Applied to Estimated Tax. https://www.irs.gov/instructions/i1040x ↩