My income fluctuates a lot so it is hard to predict. Also, I've read that I can be fined for paying too little or too much estimated taxes, so what is the amount under or over before I get fined?
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.
When paying out estimated taxes for 2018, when it comes around to file taxes for 2018, where in the Turbo Tax application can I declare how much in taxes I already paid?
If I underpaid, how much do I have to underpay to get fined?
If I overpaid, how do I reclaim the money I overpaid?
To prepare estimates for next year you need to be in your current return. You can just type W4 in the search box at the top of your return , click on Find. Then Click on Jump To and it will take you to the estimated tax payments section. Say no to changing your W-4 and the next screen will start the estimated taxes section.
OR go to
Federal on left
Other Tax Situations
Other Tax Forms
Form W-4 and Estimated Taxes - Click the Start or Update button
When you get to the W4 and Estimated Taxes section, say you want to adjust your income to go though all the screens.