What is quarterly estimated taxes?
The four payment dates hit with numbers computed from live books instead of last year’s guess.
The US doesn't let a self-employed person or a pass-through owner wait until April to settle up. If you expect to owe the IRS $1,000 or more for the year after withholding and credits, the pay-as-you-go rule kicks in and you're on the hook for four estimated payments: mid-April, mid-June, mid-September, and mid-January of the following year, each filed on Form 1040-ES. This isn't a filing in the sense of a return the IRS processes and acknowledges — it's a payment with a voucher, made through IRS Direct Pay, EFTPS, a check, or the IRS2Go mobile app, and the only thing that comes back is a payment confirmation.
The number behind each payment is where the actual work sits. It has to come from a defensible computation, not a number pulled from thin air, and the defensible version means running current-year income and deductions against the safe-harbour test: pay at least 90% of what you actually owe for the current year, or 100% of last year's total tax (110% if last year's adjusted gross income was over $150,000), and the IRS waives the underpayment penalty regardless of how the actual year turns out. Which of those two methods to lean on is a judgment call about the shape of the year — a business having a much better year than last year wants the safe-harbour percentage of last year's tax; a business winding down wants the current-year 90% test — and that call belongs to the partner CPA firm, not to a spreadsheet.
Who does what
Computed with the partner CPA firm; safe-harbour elections are their call.
Who does what
| Your CapEasy team | Quarterly estimated taxes, the reconciliations and reporting behind it, and the questions list that keeps it honest. |
| Your CPA or enrolled agent | Everything that carries a licence in United States — rendered exactly as written: issue compilation, review or audit reports — those are restricted to licensed cpa firms. |
| You | One conversation with one named person, and the decisions that are genuinely yours. |
Quarterly estimated taxes in United States
The $1,000 threshold is what pulls a taxpayer into the estimated-payment system at all
Per IRS guidance on estimated taxes, you generally have to make estimated payments if you expect to owe $1,000 or more when you file, after subtracting withholding and refundable credits. Most W-2-only taxpayers never hit this because withholding covers it; proprietors, partners, and S-Corp shareholders with no withholding on their business income cross it routinely. Whether a given client is actually over the threshold in a given year is a computation we run from live books and hand to the partner CPA firm to confirm.
The safe-harbour test is what actually prevents an underpayment penalty, not the size of the final check
Per Form 1040-ES instructions, the underpayment penalty is waived if total withholding and estimated payments for the year equal at least 90% of the current year's tax, or 100% of the prior year's tax (110% if the prior year's AGI exceeded $150,000). A taxpayer can owe a large balance at filing and still face zero penalty if the safe harbour was met on time each quarter — and can pay every voucher on time and still be penalized if the amounts fell short of both tests. We run both calculations every quarter; which one the partner CPA firm elects to rely on is their call.
The four due dates aren't even quarters, and a missed date is penalized period by period
Per irs.gov, the 2026 estimated payment dates are April 15, June 15, September 15, and January 15 of the following year — periods of roughly 3.5, 2, 3 and 4 months, not four equal calendar quarters. The IRS calculates any underpayment penalty on a period-by-period basis using Form 2210, so a shortfall in the June payment isn't cured by overpaying in September; each period is judged on what was due and paid within it.
Schedule SE self-employment tax rides on top of income tax inside the same estimate
Per IRS guidance on self-employment tax, a sole proprietor's net Schedule C earnings are subject to 15.3% self-employment tax (12.4% Social Security up to the annual wage base, plus 2.9% Medicare) in addition to ordinary income tax, and Schedule SE is what computes it. Because there's no employer withholding half of it the way a payroll job would, the full 15.3% has to be built into the quarterly estimate from the start — a common failure mode is estimating income tax alone and being caught short by the SE tax layered on top.
What your CPA or enrolled agent receives from us
- A year-to-date profit and loss pulled directly from the books, as of the date the estimate is being run — not a stale prior-period figure.
- Both safe-harbour calculations side by side: 90% of current-year projected tax, and 100%/110% of prior-year total tax, so the partner CPA firm can see which one governs and why.
- A Schedule SE self-employment tax estimate layered into the total for proprietors, computed on projected net Schedule C earnings.
- A per-period breakdown showing what was paid, what was due, and any gap, mapped to the four 1040-ES due dates for the year.
- A one-page number-and-date summary for each upcoming voucher, delivered with enough lead time to pay through Direct Pay, EFTPS, check or IRS2Go before the deadline.
- A running log of estimated payments made during the year, reconciled against what the year-end Form 1040 will need to true up.
