I understand that, to avoid potential underpayment penalties, I must pay at least 90% of tax owed for current year or 100% (or 110% for AGI threshold of $150K+) of prior year's tax owed.
TurboTax automatically calculates the 4 quarterly estimated tax payments for me based on the above.
My situation is that I am retired and have only investment income, whose stream does not come in evenly over the year. My estimate is that, instead of 25% per quarter, it is around 20% for each of the first 3 quarters and 40% for the last quarter (due to the capital gain distributions from mutual funds at the end of each December).
My first question: I can change the quarterly estimated tax payment amounts preprinted by TurboTax to more closely fit my actual income stream throughout the year. As long as the total paid for the year satisfies the minimum amount for the year as per the IRS requirements (from the first paragraph above), I should not be subject to underpayment penalty (or interest penalties). Is that correct?
A related question: In general, does the IRS (and state of California) only care that you pay the entire amount for the year by the 4th tax payment due date? Or does it actually look at your income stream during the year to figure out a quarterly amount? I don't think the latter is possible because the IRS does not have data of my income on a monthly basis.
My second question: In addition to paying quarterly, can I make 1 or 2 extra monthly payments per quarter? For example, if I am supposed to pay $30k in June for the 2nd payment, can I pay $10k in June and $20k in July? In other words, once I have determined my total estimated payment amount for the year, can I make my own payment schedule, for instance, 10 monthly payments that add up to the total amount due for the year?
