Start with 2026 Form 1040-ES. A useful estimate includes the whole return: your business, wages, spouse's income when filing jointly, investment income, deductions, credits, and payments already made.
1. Estimate business profit
Project annual receipts, then subtract eligible business expenses. Track the business portion and retain documentation. Cash spending and a tax deduction are not always equal: vehicle deductions, depreciation, and home-office methods can differ from cash outflows.
2. Calculate self-employment tax
For a sole proprietor, the usual SE earnings base is 92.35% of net business profit. Calculate the 12.4% Social Security portion using the remaining 2026 $184,500 cap after the same taxpayer's Social Security wages, then 2.9% Medicare on the SE earnings base. Additional Medicare tax may apply. IRS SE tax, SSA wage base.
As a narrow example, $100,000 of profit with no other Social Security wages produces $92,350 of SE earnings and $14,129.55 of ordinary SE tax. This is not the person's total tax bill. Half of ordinary SE tax generally reduces adjusted gross income; it does not cut the SE tax itself in half.
3. Estimate income tax on the full return
Use filing-status-specific brackets and eligible deductions. The 2026 basic standard deduction is $16,100 single or married filing separately, $24,150 head of household, and $32,200 married filing jointly, before applicable adjustments. Use credits and other taxes where relevant. 2026 Form 1040-ES.
Do not deduct retirement contributions, health insurance, or QBI automatically. Each has eligibility and calculation rules. Healthcare income generally falls within QBI's specified service business rules. IRS QBI instructions.
4. Determine the payment target
Generally, the required annual payment uses the smaller of 90% of current-year tax or 100% of prior-year tax. Use 110% for the prior-year comparison when prior-year AGI exceeds $150,000 ($75,000 if married filing separately). The prior-year return must cover 12 months. Then account for withholding and applicable credits. A balance below $1,000 after withholding and refundable credits can qualify for an exception. IRS estimated-tax rules.
Here is a simplified safe-harbor example with a full-year prior return, prior AGI below the threshold, even income and withholding, and no special rules:
| Item | Amount |
|---|---|
| Prior-year tax | $20,000 |
| Projected current-year tax | $26,000 |
| 90% of current-year tax | $23,400 |
| Smaller annual target | $20,000 |
| Expected withholding | $8,000 |
| Annual estimate amount | $12,000 |
| Four timely equal installments | $3,000 each |
Paying that target can still leave $6,000 due with the return. Safe harbor addresses the underpayment penalty, not the final tax liability.
5. Pay on the correct schedule
| 2026 payment period | Standard federal due date |
|---|---|
| January 1–March 31 | April 15, 2026 |
| April 1–May 31 | June 15, 2026 |
| June 1–August 31 | September 15, 2026 |
| September 1–December 31 | January 15, 2027 |
These periods are unequal. Uneven income may justify the annualized income installment method. Wage withholding is generally treated as paid evenly through the year unless actual timing is elected; estimated payments count when paid. Extra withholding may therefore work differently from a late estimated payment. IRS Publication 505.
Review state and local requirements separately, especially for locum work in multiple states. 1099 Ops offers planning estimates for supported situations; it does not submit a tax payment or replace this household calculation. Keep payment confirmations with the quarterly tracking routine.