The general rule is 25 to 30 percent of your net income after expenses. That range accounts for federal income tax, self-employment tax, and Arizona state income tax. The exact number depends on your total annual income, filing status, and deductions, but 25 to 30 percent keeps most owner-operators out of trouble.

Here is where that percentage comes from. Self-employment tax alone is 15.3% on the first $168,600 of net earnings for 2024. That covers both the employer and employee portions of Social Security and Medicare. Federal income tax adds another layer based on your bracket, which for most owner-operators falls somewhere between 12% and 22%. Arizona charges a flat 2.5% individual income tax rate. Stack those together and you land squarely in the 25 to 30 percent range.

The IRS expects you to pay taxes as you earn throughout the year, not in one lump sum in April. Quarterly estimated payments are due April 15, June 15, September 15, and January 15. Miss those dates or underpay significantly and you will face an underpayment penalty. That penalty applies if you owe more than $1,000 when you file your annual return. It is not a huge amount, but it adds up over multiple quarters and multiple years.

The most practical approach is opening a separate savings account dedicated to taxes. Every week, transfer 25 to 30 percent of your net earnings into that account. Weekly transfers work better than monthly because the money leaves your operating funds before you have a chance to spend it. When a quarterly payment comes due, the money is already sitting there. No scrambling, no pulling from your operating account, no missed payments.

If your income varies significantly from quarter to quarter, which is common for owner-operators in seasonal industries, you can adjust the percentage. A strong quarter might warrant setting aside 30 percent while a slower quarter might only need 25. What matters is that you are consistently putting money away rather than trying to come up with a lump sum four times a year.

Tracking your net income accurately is the foundation of all of this. If you are guessing at your expenses or not categorizing them properly, your net income number is off and your tax savings will be too. Working with Phoenix bookkeepers who understand owner-operator finances makes a real difference here. Clean books mean you know your actual net income every week, which means your tax savings percentage is based on real numbers instead of rough estimates.

One more thing worth mentioning. Your quarterly payments should be based on what you expect to owe for the current year, not just what you paid last year. If your business is growing, last year’s numbers will leave you short. If you want help estimating your liability or filing accurately, business tax return preparation from someone who understands your situation can prevent expensive surprises at filing time.