How do estimated tax and self employment tax work for a US sole proprietor?
Income without withholding is paid in four estimated instalments during the year, and net earnings from self employment carry the social security and medicare contributions on top of income tax. Underpayment triggers an addition to tax even where the return is filed on time.
The answer differs between the federal level and the states, see the rows below.
The answer by level
Federal level
Estimated tax is paid in four instalments during the year by a person who expects to owe tax when the return is filed and does not have enough withheld.
Form 1040-ES, Estimated Tax for IndividualsTax treatment
Self employment tax covers the social security and medicare contributions of a person who works for their own account, and is computed on the net earnings from that work.
Schedule SE, self-employment tax, 26 U.S.C. § 1401Threshold
Whether a business counts as small for federal programmes and set asides is determined by the size standards, measured by receipts or employees per industry code.
13 CFR Part 121, small business size regulations
Source lines
- Estimated tax applies where the taxpayer expects to owe tax and withholding does not cover it.
- Self employment tax is computed on net earnings from the trade or business, separately from income tax.
- Federal size standards define small business by receipts or employees per industry code, which controls access to set asides.
What it means for the company
The instalments are budget items, not year end events. Setting aside each payment when the invoice is received is what prevents the underpayment addition.
| Level | Requirement | Source |
|---|---|---|
| Federal level | Estimated tax is paid in four instalments during the year by a person who expects to owe tax when the return is filed and does not have enough withheld. | Form 1040-ES, Estimated Tax for Individuals |
| Tax treatment | Self employment tax covers the social security and medicare contributions of a person who works for their own account, and is computed on the net earnings from that work. | Schedule SE, self-employment tax, 26 U.S.C. § 1401 |
| Threshold | Whether a business counts as small for federal programmes and set asides is determined by the size standards, measured by receipts or employees per industry code. | 13 CFR Part 121, small business size regulations |
What it means for the individual
A sole proprietor pays both halves of the contributions that an employer and employee would otherwise split.
Source lines
- Internal Revenue ServiceForm 1040-ES, Estimated Tax for Individuals · read 2026-08-25 · proof 60f7f4275cf3494cOfficial source
- Internal Revenue ServiceSchedule SE, self-employment tax, 26 U.S.C. § 1401 · read 2026-08-25 · proof 60f7f4275cf3494cOfficial source
- Electronic Code of Federal Regulations13 CFR Part 121, small business size regulations · read 2026-08-25 · proof 60f7f4275cf3494cOfficial source
Next step
Calculate the annual estimate at the start of the year, diarise the four dates, and revise the estimate after any quarter with unusual income.
This page reports what the sources say, with the identifier and address of the publisher. It is not legal advice and does not decide an individual matter.
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