1099

 Estimated tax payments are based on an estimation of your income for the current year.   Through your employment W-2 your Federal withholding counts as payments made for you.   However; with the independent contractor work you will need to estimate your income less related expenses.   

The tax caster link below will guide you through to estimate your tax liability which is comprised of your wages along with your self employment income:

Here is a link to tax caster to assist in calculating your Federal Tax:   https://turbotax.intuit.com/tax-tools/calculators/taxcaster/

If you need to remit additional payments you will use form 1040ES and/or increase your federal withholding through your employer to cover and shortage.

Estimated tax payments IRS 1040ES tips 

Estimated tax payments are due four times in a tax year. For calendar year taxpayers (which is most individuals), the due dates are April 15, June 15, September 15 of the current year and January 15 of the following year or the next business day if the due date falls on a weekend or holiday.

Be sure to check on your state estimates - the state website should have that information.