If you publish a book yourself, your income from book sales is considered self-employment income, according to the Independent Book Publishers Association. You must declare this income on Schedule C, a form you attach to your tax return to document profits and losses in your business over the past year. Self-employment income is taxed at a rate of 15.3 percent, and if you make over $400 in a year, you are required to file estimated taxes on a quarterly basis.
Book publishers may use either the cash or accrual accounting methods to determine their income for the year. The accrual method requires the publisher to count income she should have received during the tax year even if she will not actually receive the income until the following tax year. Very successful publishers--those who earn more than $1 million per year--must use this method. All other book publishers are free to use the cash method, which requires them to report only income actually received in a given tax year when filing taxes for that year.
Book sales are considered ordinary income for tax purposes and must be reported as such. Ordinary income is any income resulting from business activities such as the sale of books. If a publisher receives a grant to publish or promote certain types of books, the grant is considered earned income and is taxed at a lower rate.