i received a CP2000 with a proposed amount from the IRS, but they calculated the securities sales without cost-basis, and so the amount they proposed was too high. this was easy to correct in TurboTax online (i had indeed forgotten to report it, as i had properly done in 2018 and 2020.) i want to pay the penalty and interest to stop the clock running on the interest, but if i go through TurboTax, i don't see a way to indicate adding the penalty and interest to the payment.
NO ... there is no way to add penalties and interest. The IRS/State will mail you a bill later after they have processed the return.
The clock stops when the IRS receives your payment of the amount due on the amended return. Mail it by certified mail with a return receipt so you will have tracking and confirmation of delivery.
TurboTax cannot calculate the penalty and interest. One reason is that it has no way of knowing when the IRS will receive your payment. Also, there is no place for the penalty and interest on the amended return form (Form 1040-X), so even if TurboTax could calculate it, it would have no place to put it.
The IRS will send you a bill for the penalty and interest. Just make sure you pay it by the due date on the bill. If the amount is small, they might not bother to bill you.
Penalties:
Subtract any penalty (line 38) from the amount you owe reported on original 1040.
Don't try to include, but ignore, any new or changed penalty.
IRS will calculate your new penalty on their own and will bill you.
fastest way for the IRS to get paid is to use its online portal
https://www.irs.gov/payments/direct-pay
If you think to pay ahead will help you, pay now on IRS direct pay and include that amount on line 16 of the 1040-X that you file.
I withdraw this suggestion !
sorry @Critter-3