If you are self employed how do you determine the amount to send to IRS quartly if you want a refund

It depends. The IRS has published an worksheet for you to prepare your estimated taxes. This can be found here. Here are the steps listed in Worksheet 2-1.2024 Estimated Tax Worksheet in the link..

Step 1: Estimate Your Annual Income

• Estimate your total income for the year (including self-employment income, investment income, etc.).
• Factor in any business expenses you plan to deduct (for example, operating expenses, home office deductions, etc.).

Step 2: Calculate Your Estimated Tax Liability

To calculate your estimated taxes, you need to know your estimated net income (income after expenses), and then apply the self-employment tax and income tax:

Self-Employment Tax: This is the tax that covers Social Security and Medicare. It is calculated on your net earnings from self-employment, which is generally 92.35% of your net income (since you deduct half of your self-employment tax when calculating your adjusted gross income).

• Self-employment tax rate: 15.3% (12.4% for Social Security and 2.9% for Medicare).Then 
• For income above a certain threshold ($200,000 for individuals, $250,000 for married couples), an additional 0.9% Medicare tax may apply.

Income Tax: Your net income after deducting any allowable expenses will be taxed at the applicable income tax rate based on your tax bracket. You can refer to the IRS tax brackets for your filing status (e.g., single, married filing jointly, etc.).

Also you would factor any credits you may expect to receive during the year if you qualify such as the child tax credit, earned income credit if you are eligible for any of these.

Step 3: Calculate Your Quarterly Payments

Use IRS Form 1040-ES: The IRS provides Form 1040-ES for calculating and paying estimated taxes. You can use the worksheet included with the form to estimate your taxes for the year.

Formula to estimate quarterly payments:

• Estimate your total tax liability for the year (including self-employment tax and income tax).
• Divide this by 4 to determine the amount you should pay each quarter.

This should give you a guideline on how to get started.