@bhuether
1. The IRS annualizes your income, although if you file form 2210 properly, you can reduce the effect. However, if you don't annualize your income, the entire payment was due June 15, and the entire amount is past due on Sept 15 and January 15. Annualization may be in your favor in this case. I can't tell for sure without doing a lot of calculations.
2. Your tax liability for 2020 is line 24 of form 1040. Your tax liability for 2021 would also be line 24 of your 2021 return. (Your tax liability is what you actually pay to the government regardless of when you pay it. If you had $5000 of payments and got a $1000 refund, your liability was $4000. If you had $5000 of withholding and payments and owed a further $1000, your tax liability was $6000.)
For 2021, you need to pay up to 90% of your 2021 liability, or 110% of your 2020 liability, to avoid an underpayment penalty. It sounds like your 2020 income was probably much lower than 2021, so I wonder if you can make an estimated payment now that will bring your total of 2021 withholding and payments up to 110% of your 2020 amount. That will block the underpayment penalty, and probably interest, from accruing before April 18, 2022.
After April 18, 2022, you will be liable for a failure to pay on time penalty, which is the same terms as the underpayment penalty (0.5% per month plus interest). The failure to pay penalty is assessed even if you have an extension to file, because April 18 is also the payment deadline and a filing extension is not a payment extension (there are no payments extensions, in fact). But, if you can afford to make a payment now based on your 2020 information, that will make sure that the penalty and interest clock starts on April 18, 2022 and not June 15, 2021.
3. That depends on how much you really owe. Taking account of all your withholding and payments so far, how much more would you have to pay by February 15 to get the total to equal 110% of your 2020 line 24?
4. Only you can make that decision given your total facts and circumstances (as well as the ability to work other jobs, etc.)
5. "Curious: Does the IRS have an online tool that lets you see in real time your debt status (penalties, interest, etc)?" Yes, you can review your account online, although I don't know how often it's updated. And for now, it won't show a balance because you haven't filed.
https://www.irs.gov/payments/your-online-account
Two other points to be aware of:
6. If you are "permanently and totally disabled" under IRS regulations, you are exempt from the additional 10% penalty on early IRA withdrawals. For the IRS, permanently and totally disabled means unable to perform substantial gainful employment. This is not necessarily the same thing as a VA disability, because some forms of medical disability will still allow you to work. Only you or your doctor can determine if you qualify for being disabled for income tax purposes.
7. If you make an IRA withdrawal directly to the IRS to pay a tax debt, that is also exempt from the 10% penalty for early withdrawals. So I would probably not make any IRA withdrawals to pay income taxes, until you have your OIC or payment plan, and you can arrange a direct transfer to the IRS. Your money would go a little farther that way.
