TurboTax can compute these for you, as described in the FAQ
below. It's possible that you can be
penalized for underpaying estimated taxes, but not for overpaying.
https://ttlc.intuit.com/replies/3301730
If you're more comfortable computing estimated taxes
yourself, please see this IRS page on Estimated
Taxes, and 2017 Form
1040-ES, Estimated Tax for Individuals.
