How do you guys make the right estimated tax payments to avoid paying underpayment penalty given the volatile and unpredictable nature of trading for living? I trade full-time (not qualified for TTS). I didn't make much money and got a refund in 2016. My profit spiked in 2017 (AGI ~$120k) but I still made the same estimated tax payments as 2016 so I'm pretty sure I'm underpaying and owe tax at this point. Do I have to pay a underpayment penalty or I'm exempt from it this year? Should I make a big estimated tax payment on January 16 or wait till I file my tax in April? Thanks!