- Sole proprietor or single-member LLC: business income flows onto Schedule C of your personal return, due April 15
- S corporation: a separate Form 1120-S due March 15, and you must pay yourself reasonable compensation through payroll
- Self-employment tax covers Social Security and Medicare, and it is on top of income tax rather than inside it
- Quarterly estimated payments on Form 1040-ES, due April 15, June 15, September 15 and January 15, with penalties for underpaying even if you settle up in April
- State income tax on top, except in states with none, such as Texas and Florida
- Sales tax where you have nexus, which since Wayfair can include states you have never set foot in
- Form 1099-NEC to each noncorporate contractor you paid $2,000 or more for services in 2026 by cash, check or bank transfer (card payments go on Form 1099-K), due February 1, 2027 because January 31 falls on a Sunday (As of Oct 2026)
Quarterly, Form 1040-ES: April, June, September and January. Underpaying carries a penalty even if you settle in April.
Annual, Schedule C with your personal return.
Self-employment tax on top of income tax, which is the one that surprises people.
Colorado state income tax, with its own filing.
Sales tax if what you sell is taxable in Colorado, which is home rule, so cities administer their own. That is the messy one.
Set aside a percentage of every payment as it lands. Want me to work out the percentage for your numbers?
It named Colorado home rule sales tax, which is a genuinely local trap.
Self-employment tax
Net earnings are 92.35% of net profit. Social Security takes 12.4% of that up to the 2026 wage base of $184,500, and Medicare 2.9% of all of it, plus 0.9% Additional Medicare above $200,000 for a single filer. Half the tax, excluding the 0.9%, is deductible. On $95,000 of profit, self-employment tax is $13,423.07. As of Oct 2026.
IRC secs. 1401, 1402 and 164(f)
Estimated tax and the safe harbors
Estimates are required when you will owe $1,000 or more after withholding and credits. There is no underpayment penalty if each installment is at least 25% of the lower of 90% of this year's tax or 100% of last year's, or 110% of last year's if last year's AGI was over $150,000. A due date on a weekend or legal holiday moves to the next business day. As of Oct 2026.
IRC secs. 6654 and 7503; IRS Form 1040-ES
| April 15, 2026 | $4,950 |
| June 15, 2026 | $4,950 |
| September 15, 2026 | $4,950 |
| January 15, 2027 | $4,950 |
| 110% of last year's tax | $19,800 |
| Each installment | $4,950 |
AGI was over $150,000, so the safe harbor is 110% of $18,000. You still settle any balance in April, but no underpayment penalty applies however the year turns out.
If you run payroll, add Form 941 by the last day of the month after each quarter, and Forms W-2 and 940 by January 31, which for the 2026 forms is February 1, 2027 (As of Oct 2026).
The amount is the same either way. Only one version involves a scramble.
The IRS is expected to publish its 2027 inflation adjustments in October or November 2026. Ask MARCUS to recheck your figures when it does.
I run a [type of business] in [state], set up as a [sole proprietor, single-member LLC, S corp], with revenue of roughly [amount] and profit of roughly [amount] a year. Last year's federal tax was [amount]. Give me a simple calendar of what is due and when, federal and state, and what to pay each quarter.
Every lesson ends with a question to hand to a Greymill specialist, who answers with what it knows about your business.
More in Cash, tax and getting paid
- Where the money actually goesBusy, profitable on paper, and the account never grows.Read the lesson
- When a customer will not payThere is an order to this, and skipping to the end costs you money.Read the lesson
- When a customer will not payThere is an order to this, and skipping to the end costs you money.Read the lesson
- Knowing what is due and whenNothing about tax is difficult. It is the surprise that hurts.Read the lesson
- What you can and cannot claimMost people either claim nothing out of fear, or everything out of hope.Read the lesson
- When the books are months behindEveryone gets here. The way out is not to do it all in one weekend.Read the lesson