Stock Options

Hello

 

I left my employer in January and decided to retire.

 

I sold the stock options from the former employer in June and got about $4M proceed. They are all qualified for the long-term investment.

 

I live in Hawaii. So, I assume I must pay 20% to Federal and 7.25% Hawaii as the long-term capital gain tax.

 

Questions:

  1. Is my understanding correct?
  2. How do I calculate how much I should pay by 9/16 and 1/15?
  3. If I sell more stock options later in this year, for example additional proceed of $500K, how do I calculate and change the estimated tax amount?
  4. How can I make the estimated tax for Fed and HI? Is there any online links?
  5. If I miss the deadline (9/16 and 1/15) can I still pay the estimated tax later like 9/31 and 1/31?
  6. What is the penalty of not paying the estimated tax until I file the 2024 tax by 4/15?