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"How does the IRS know which method I am using?"
Your Schedule C determines what method you are using by your marking on the Schedule the method. that is line F on the Schedule C.
"What should be the recognize method from the IRS if I am using two methods?"
The Hybrid Method.
Generally, you can use any combination of cash, accrual, and special methods of accounting if the combination clearly reflects your income and you use it consistently.
However, the following restrictions apply.
If an inventory is necessary to account for your income, you must use an accrual method for purchases and sales
. See Exceptions under Inventories, later. Generally, you can use the cash method for all other items of income and expenses. See Inventories, later.
If you use the cash method for reporting your income, you must use the cash method for reporting your expenses.
If you use an accrual method for reporting your expenses, you must use an accrual method for figuring your income.
Any combination that includes the cash method is treated as the cash method for purposes of section 448 of the Internal Revenue Code