Which form is primarily used for reporting income from self-employment?

The form primarily used for reporting income from self-employment is Form 1040 Schedule C. This form is specifically designed for sole proprietors to report income and expenses related to their business activities. It provides a detailed account of business income, as well as allowable business deductions, which ultimately helps to calculate the net profit or loss from self-employment that is carried over to the individual's Form 1040 tax return.

Form 1065, while related to business income, is used for partnerships to report income, deductions, and credits from the partnership's operations, not for individual self-employed income. Form 941 is a quarterly tax return used to report employment taxes, while Form W-4 is a form provided to employers by employees to determine the amount of tax withholding from their paychecks. None of these forms serve the purpose of reporting income from self-employment like Schedule C does.