Quarterly estimated taxes: avoiding the year-end shock
Tax isn't a once-a-year event for most growing businesses. Here is how quarterly estimated payments work, how to size them, and how to stop a surprise bill in April.
If you've ever sat across from your accountant in March and heard a number you weren't ready for, you already understand the problem. When you own a business or earn income that flows straight to your personal return, nobody is quietly setting aside tax money for you. That job is yours now—and the IRS expects you to do it four times a year, not once.
For employees, taxes are invisible. Every paycheck has income tax withheld before the money ever lands, so by April the bill is mostly settled. When you're self-employed or your company is a pass-through—meaning the profit "passes through" to your personal tax return, as it does with an S corporation, partnership, or sole proprietorship—that withholding disappears. The money hits your account in full, untaxed, and it's easy to spend as if it's all yours.
It isn't. The tax is still owed; you're just paying it on your own schedule. The IRS calls this pay-as-you-go, and it runs on a simple idea: you should hand over tax roughly as you earn the income, not in one lump at year-end.
The four dates that run your year
Estimated taxes are due in four installments, and they don't line up neatly with calendar quarters. Payments fall around mid-April, mid-June, mid-September, and mid-January of the following year. That third gap is short and the fourth is long, which trips up plenty of owners who assume the money is due every three months like clockwork.
Put these dates in your calendar now, with a reminder a week ahead of each one. A missed installment isn't forgiven just because you catch up later—the clock on what you owe starts the day a payment is late.
How much to send
You don't have to predict your exact tax bill to stay out of trouble. The IRS offers a "safe harbor"—a target that, if you hit it, shields you from underpayment penalties even if you end up owing more at filing. The general rule is to pay in either a set percentage of last year's total tax or roughly 90% of this year's. Higher earners face a higher last-year threshold. The exact percentages and the income line where they shift change over time, so confirm the current figures with your tax advisor before you lock in your numbers.
Last year's tax is usually the easier target because it's a fixed, known number—take it off your prior return, divide by four, and pay that each period. The catch is that if your income jumps sharply this year, hitting only last year's amount keeps you penalty-safe but leaves a real balance due in April. Plan for that gap so it doesn't surprise you.
There's a simpler habit that keeps most owners ahead of all of this:
- Open a separate savings account used only for taxes.
- Each month, move a fixed share of your profit into it—many owners start near 25% to 30% and adjust with their advisor.
- When a due date arrives, pay the estimate straight from that account.
- Never touch the balance for payroll, inventory, or anything else.
Do this and the quarterly payment stops feeling like a hit. The money was never in your operating cash to begin with—it was always the government's, just parked where you couldn't accidentally spend it.
What you pay if you skip it
Underpay, and the IRS charges what is effectively interest on the shortfall, calculated from each missed due date until you pay. It's not a flat fine you can shrug off—the rate resets periodically and has climbed in recent years, so a meaningful underpayment can cost real money on top of the tax itself. Paying on time isn't about being a good citizen; it's the cheapest option available to you.
Don't forget your state
Most states with an income tax run their own estimated-payment system, with their own due dates and their own penalties. A founder who carefully covers the federal side and ignores the state can still get a bill they didn't budget for. If you operate in a state that taxes income, set aside for both and track both calendars together.
The single best move you can make this week is to open that dedicated tax account and start funding it from your next deposit—then sit down with your advisor to confirm your safe-harbor target and the exact state and federal due dates for the year.
The tax was never your money—park it before you spend it.