If I have already paid my estimated taxes for all 4 pay periods, and say I earn capital gains by sale of stock (say mid-year), do I have to pay additional taxes?

[jaykothari]

In June I paid all my Estimated Taxes for the year. In August I earned high capital gains via stock sale. My question is do I have to pay additional taxes (before September 15) or I can pay all together by April 2021?

[Anonymous · Accepted solution]

there are exceptions to an underpayment penalty. 

1) withholding and timely estimated tax payments = 90% of 2020 tax or

2) withholding and timely estimated tax penalties = 100% of 2019 tax (110% if adjusted gross income for 2019 was over $150,000

3) 2020 tax less withholding is less than $1000

state tax laws will vary from the above

this means for federal purposes if you meet any of the 3 exceptions above, you could owe a substantial amount come 4/15/2021 and not be hit with underpayment penalties. 

[Carl]

There is no requirement that says you *have* to pay 4 quarterly taxes, or that you can "only" pay 4 quarterly tax payments. You can make tax payments to the IRS every week of the year if you want. So if you need to make another payment to avoid any underpayment penalties, do so.

Generally speaking if at tax filing time you owe the IRS more money, if what you owe is less than $1000 or less than 10% of your total tax liability (whichever is *HIGHER*) then no underpayment penalties are assessed. There are exceptions and other factors as already pointed out by others in this thread. But to avoid additional paperwork, you might want to pay more.

In other words, it's your call.