Deducting over-payment of 2020 Federal taxes from first 2021 estimated payment

[Periwinkle65]

I know it is acceptable to deduct an over-payment of last year's Federal taxes from the first estimated tax payment of the current year. I would be making the first 2021 estimated payment on April 15, 2021 as required.  My only uncertainty is whether this can be done if I file my 2020 taxes-- as allowed-- on May 17 of this year. I would probably add a bit to that payment to allow for any minor corrections made on the 1040 forms.  I 

[DavidD66]

If you choose to use your refund toward your estimated taxes, the refund amount will apply to your first estimated tax payment, even if you file on May 17.

[Periwinkle65]

Thanks for your helpful response. I am also wondering whether I can deduct a little less than the refundable amount and catch up on the remainder of the refund on my 2nd estimated payment?  I may not be entirely certain of the final amount of that refund until I file in May. I would not want to under-pay. 

[gloriah5200]

Generally, if you ask IRS to keep your refund toward the next year's estimated payments, then they will apply the entire amount toward the first estimated payment.  If it is more than is needed, then it will just have excess applied to the first payment.  You can then reduce the remaining payments so that the total is still paid in while the income is being earned so you don't have an underpayment penalty in any quarter.

You can still pay an additional estimated payment amount if you wish, to be safe.