The calculation runs in three stages, then converts the result into a quarterly estimated-tax payment.
The 2026 Social Security wage base is $184,500, per the SSA Contribution and Benefit Base page. Self-employment tax runs at 15.3% on 92.35% of net profit, per IRS Topic No. 554. Half of that SE tax reduces AGI as an above-the-line deduction confirmed by the same topic.
The 2026 federal standard deduction for single filers is $16,100, and the federal brackets range from 10% on income up to $12,400 through 37% above $640,600, both from Rev. Proc. 2025-32. North Carolina's 2026 flat individual income tax rate is 3.99%, per the NCDOR Tax Rate Schedules, and the NC standard deduction for a single filer is $12,750, per the NCDOR 2025 D-401 instructions. [TODO: verify NCDOR D-401 TY2026.]
These calculations are estimates for educational and planning purposes only, not tax, legal, or financial advice. Tax rules change, edge cases exist, and your specific situation may include factors this calculator does not model. Always confirm figures against the current IRS guidance and your own records before filing or making a financial decision, and consult a qualified tax professional, CPA, or enrolled agent for advice tailored to your circumstances.