Estimated Quarterly Taxes: What to Pay, When, and Why It Matters

If you own a small business and you aren't making quarterly estimated tax payments, you could be in for an unwelcome surprise — and possibly a penalty — when you file your annual return. The IRS expects you to pay taxes as you earn income throughout the year, not just in one lump sum every April. Here's how quarterly estimated taxes work and how to handle them without scrambling.

Who Needs to Make Estimated Tax Payments?

When you work as an employee, your employer withholds income tax and payroll tax from each paycheck and sends it to the IRS on your behalf. When you're self-employed or own a business, no one withholds for you. The IRS requires you to make estimated payments four times a year to cover both income tax and self-employment tax — the self-employed version of Social Security and Medicare.

This applies to sole proprietors, single-member LLCs, partners, and S corporation shareholders. The general rule: if you expect to owe at least $1,000 in tax for the year after subtracting your withholding and credits, you should be making quarterly payments.

If you also have a W-2 job (or your spouse does), you may be able to increase withholding there instead of making separate estimated payments. Talk to a tax pro about which approach works better for your situation.

The Four Quarterly Deadlines

Estimated payments don't follow a clean quarterly schedule, which is why people miss deadlines. Here are the due dates:

• Q1 (income from January–March): due April 15
• Q2 (income from April–May): due June 15
• Q3 (income from June–August): due September 15
• Q4 (income from September–December): due January 15 of the following year

The second payment covers only two months, not three. That short window catches business owners off guard every year. If a due date lands on a weekend or federal holiday, it shifts to the next business day.

How to Calculate Your Payment

There are two common approaches.

Use last year's tax as a baseline. If your income is fairly steady, divide your total tax liability from last year's return by four and pay that amount each quarter. Paying at least 100% of last year's total tax (or 110% if your income was above a certain threshold — check current IRS rules) generally protects you from underpayment penalties, even if you end up owing more.

Estimate based on current-year profit. If your income swings significantly from year to year, estimate your profit for the current year, calculate the projected tax, and divide by four. This is more accurate but requires up-to-date books. If your profit rises or falls sharply mid-year, you can adjust the next payment up or down.

Many business owners blend both methods: pay the safe-harbor amount based on last year, then increase payments if current-year profit is trending higher.

What Happens If You Don't Pay Enough

The IRS charges an underpayment penalty — essentially interest on the amount you should have paid during the year. The calculation is based on how much you underpaid and how long it was overdue.

The bigger problem for most owners isn't the penalty. It's cash flow. If you go all year without setting money aside and then get a large tax bill in April, you may not have the cash to cover it. That's how business owners end up on IRS payment plans, which add their own interest and penalties on top of what you already owe.

Practical Habits That Make This Easier

Move money into a tax savings account as you get paid. Every time a client pays you, transfer a portion of that payment into a separate account reserved for taxes. You owe tax on profit, not gross revenue, so the exact percentage depends on your margins and deductions. But if the money is already set aside, you won't be scrambling when a quarterly deadline hits.

Keep your books current. You can't accurately estimate quarterly payments if you don't know what your profit looks like. If your bookkeeping is months behind, you're guessing. Monthly reconciliation and clean expense categorization give you real numbers to work with.

Review mid-year. Around June or July, look at your year-to-date profit. If it's running well ahead of last year, bump up your Q3 and Q4 payments. If it's lower, you may be able to reduce them. A mid-year check prevents both overpaying (tying up cash you need) and underpaying (setting up a penalty).

Work with a tax professional. An accountant or enrolled agent can help you calculate payments, adjust them as your income changes, and make sure you're claiming deductions that lower your taxable profit. If you also owe state estimated taxes, they can handle both.

How to Actually Make a Payment

You can pay online through IRS Direct Pay or the Electronic Federal Tax Payment System (EFTPS). Both are free and give you a confirmation number immediately. You can also mail a check with Form 1040-ES, but electronic payments are faster and easier to track.

If bookkeeping is what's holding you back from staying on top of quarterly taxes, TwoDayBooks keeps your books clean and current so you always know your numbers when a deadline is coming.