Both will go on your personal tax return so the quarterly estimated payments will apply to both. You should consider your W2 wages and also the withholding from it. The Net Profit from your self employment will increase your total income and income tax in addition to the 15.3% Self Employment Tax. If your self employment income isn't too much you can increase your W2 withholding to cover it.
You send in quarterly estimated payments to cover the self employment tax (FICA). The Self Employment tax (Scheduled SE) is automatically generated if a person has $400 or more of net profit from self-employment. You pay 15.3% SE tax on 92.35% of your Net Profit (If it is greater than $400). The 15.3% self employed SE Tax is to pay both the employer part and employee part of Social Security and Medicare. So you get social security credit for it when you retire.
How to make the Estimated payments
https://ttlc.intuit.com/community/tax-payments/help/how-do-i-make-estimated-tax-payments/00/25875
Here are the blank Estimates and instructions…..
https://www.irs.gov/pub/irs-pdf/f1040es.pdf
To prepare estimates for next year you need to be in your current return. If you can't get your return open, Try this, you can sign back onto your account, click on Add a State. This should get you back into your return. Be very careful not to change anything in your actual 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 Taxes or Personal (Home&Business version)
Other Tax Situations
Other Tax Forms
Form W-4 and Estimated Taxes - Click the Start or Update button
Say No to W4. When you get to the W4 and Estimated Taxes section, say you want to adjust your income to go though all the screens.
