I used the 100% safe harbor to figure my estimated tax for 2017 but recently had a big stock sale. Do I need to recompute my remaining estimated tax payments?

If you rely on the 100% safe harbor (basing your 2017 estimates on 100% of your 2016 tax liability), you do not have to make adjustments during the year for any changes in income. However, as a practical matter, be prepared to pony up the unpaid taxes on your increased income. It may be advisable to increase remaining estimates so you don’t have a big payment when you file your return. It’s entirely up to you.