Unlike an employee, an individual that is self-employed will be responsible for the payment of their own withholding taxes. Although, the party that is paying the invoice will be required to file IRS Form 1099 at the end of the fiscal year if payments accrue to over $600 annually (unless the payment is for royalties which have a minimum of $10).
IRS Form 1040-ES – Self-employed individuals must file this every quarter if they should anticipate their tax obligation to be more than $1,000 per filing quarter. Even though official filing with the IRS is not due until the end of the fiscal year, the government requires that their money is paid every quarter (April 15, June 15, September 15, and January 15).