Estimated taxes: the bill nobody forecasts

There is a specific kind of bad quarter that only happens to businesses doing well. Revenue is up, margins hold, the year is going better than planned — and then a quarterly tax payment lands and the bank balance falls off a cliff.

It catches people because estimated taxes are almost perfectly designed to be forgotten. They scale with profit, so the better the year the bigger the surprise. They land quarterly rather than monthly, so they never become routine. And for a pass-through entity they do not appear on the P&L at all — the business earns the profit, and you personally owe the tax.

Why it is invisible in your books

If you run an S corp, partnership, or LLC taxed as either, the business does not pay income tax. The profit passes through to your personal return and you pay it there. So your company P&L shows a healthy net income with no tax line beneath it, and nothing in the accounting system ever mentions the payment you are about to make.

The cash, though, generally comes out of the business — usually as a distribution to fund the payment. Real money leaves, and no report you look at monthly predicted it.

The mechanism that fixes it

Open a second bank account and move a fixed percentage of every deposit into it. That is the whole solution, and it works because it converts an annual discipline problem into an automatic one.

The percentage depends on your bracket, state, and entity, so ask your accountant for a number rather than guessing — but somewhere between 25% and 35% of profit is a common starting point for a profitable pass-through. Transfer it the day money arrives, and treat that account as though it belongs to someone else, because it does.

Paying at filing is not an option

A common misconception is that estimated payments are a convenience and you can simply settle up when you file. You cannot, not without cost. The system expects tax to be paid roughly as income is earned, and underpaying through the year triggers a penalty even if you pay the full amount on time at filing.

There are safe-harbour rules that protect you if you pay at least a set percentage of last year's liability, which is genuinely useful in a year where income is growing fast — you can pay based on the smaller prior-year number and settle the difference at filing without penalty. Worth asking your accountant which safe harbour applies to you, because it can free up meaningful cash during a growth year.

Put it in the forecast, not just the account

Reserving fixes the cash. Forecasting fixes the planning. Those four payments belong in your 13-week cash flow as scheduled outflows on their actual dates, the same as rent or payroll.

This matters most when a tax date sits near something else large. A quarterly payment in the same fortnight as an inventory buy or an annual insurance renewal is how an otherwise comfortable business ends up drawing on a line of credit. Neither payment is a surprise on its own; the collision is, and only a forecast shows it.

And when profit runs meaningfully ahead of plan, revisit the reserve mid-year rather than at year end. A great year quietly increases the bill the whole time it is happening.