The Q3 estimate is due September 15. Most firms are guessing it.

Every firm sends the same reminder in early September: *"Your third-quarter estimated payment is due September 15."* And most of the estimates that go out with that reminder are the same number that went out in June and April, because it's the number from last year's return divided by four.

We run an accounting firm. We did it that way for years. Here's what we eventually admitted: an estimated payment is a bookkeeping number, and a firm that can't produce a current one is telling the client something about the books, not about the tax.

Safe harbor is a floor, not an estimate

The safe-harbor rules exist so the client avoids the underpayment penalty: pay in 100% of last year's tax (110% if adjusted gross income was over $150,000), or 90% of this year's, and the penalty goes away. Most firms run the first option because it needs nothing from the current year. It's a perfectly good way to avoid a penalty. It's a terrible way to tell a client what they owe.

A client whose business is up 40% this year will make the safe-harbor payments, avoid the penalty, and then owe a five-figure balance in April that nobody warned them about. A client whose business is down will overpay all year and float the Treasury an interest-free loan while their line of credit is drawn. In both cases the firm "did the estimates." In both cases the client experiences the firm as the people who didn't see it coming.

What a real Q3 estimate needs

To compute the September payment from actual numbers, the firm needs, for the client's business, through August:

• Closed books through the prior month. Reconciled to the statement, nothing parked in Uncategorized, owner draws and distributions booked as what they are. If July isn't closed by early September, the estimate is a guess dressed up as a calculation.
• Year-to-date net income by entity, because an S-corp owner's estimate depends on the pass-through income, not on what they took out.
• Owner compensation year-to-date and what's been withheld on it, because for S-corp owners the fastest correction to an underpayment is a payroll withholding adjustment in Q4, which counts as paid evenly through the year.
• Anything unusual in the pipeline: a property sale, a large equipment purchase that will be expensed, a bonus depreciation election, a K-1 from another entity.

None of that is exotic. All of it is unavailable at most firms in September, because the last real look at the client's books was in March.

The annualization trick almost nobody uses

The IRS lets the client compute each quarter's payment from income actually earned through that quarter, annualized. That's Schedule AI on Form 2210. A seasonal business, a business that had a slow first half, or a real estate investor whose sale closes in Q4 can pay less in the early quarters and more later without penalty, *if* the firm can show the year-to-date income at each quarter end. It's the single biggest cash-flow lever in estimated taxes, and it's only available to firms whose books are current at each quarter end. Which is the point.

What "the estimate is a byproduct" looks like

At a firm where the close runs monthly, the September estimate takes about fifteen minutes per client:

1. Pull year-to-date net income by entity through August, plus owner comp and withholding to date.
2. Project the remaining four months using the run rate, adjusted for anything the client has flagged.
3. Compute the tax on the projected year, subtract what's been paid and withheld, and split the balance across the remaining payments. Compare to safe harbor and tell the client which one you're recommending and why.
4. Send the client the number, the one-paragraph explanation, and the payment voucher or the EFTPS instruction.

Step 4 is the product. The client hears "your business is up 38% through August, so we're moving your September payment from $4,200 to $7,900 so April isn't a surprise." That sentence is worth more to the client than the return itself, and it's only possible because the books were closed.

Where Woven stands

Disclosure: Woven is our product. The reason estimates are easy for our own firm is that every client's books are closed on a monthly cadence with a visible status, so year-to-date income by entity is a report, not a project. The owner-compensation and distribution activity is booked as what it is at the time of the transaction, and multi-entity clients roll up under one view, so the pass-through picture for an owner with three entities is one screen. Woven doesn't prepare the estimate or the return. It makes the numbers the estimate depends on available in September instead of March.

The short version

• Safe harbor avoids the penalty. It doesn't tell the client what they owe. Firms that only run safe harbor are the firms whose clients get April surprises.
• A real Q3 estimate needs closed books through the prior month, YTD income by entity, and owner comp and withholding to date.
• Annualized income (Form 2210, Schedule AI) is the biggest cash-flow lever in estimates, and it's only available if the books are current at each quarter end.
• Where the close runs monthly, the estimate is fifteen minutes and a sentence the client remembers. Where it doesn't, it's last year's number divided by four.

If your September estimates are last year's number divided by four, [book a demo](/demo). We'll show you the monthly close status and the year-to-date view the estimate comes from.