All income from all sources must be reported on your tax return if you are required to file a tax return. If your only income is from this self employment job and the total is less than $400, you would not be required to file a tax return. If it is more than $400, you must file a return to pay self employment taxes even if you owe no federal income tax.
You can use IRS direct pay to pay quarterly estimates of taxes owed. Here is a link: https://www.irs.gov/payments/direct-pay
You can use the TurboTax TaxCaster to estimate how much tax you will owe: https://www.irs.gov/payments/direct-pay
There can be a penalty if you don't pay enough taxes during the year. Generally, most taxpayers will avoid this penalty if they either owe less than $1,000 in tax after subtracting their withholding and estimated tax payments, or if they paid at least 90% of the tax for the current year or 100% of the tax shown on the return for the prior year, whichever is smaller. The amount is 110% of the tax shown on the return for a prior year AGI of more than $150,000.
