Quarterly Estimated Taxes: Stop the April Surprise

Every year, contractors and small business owners get hit with a large April tax bill — plus penalties — because they didn't pay enough during the year. The good news: it's almost entirely avoidable.

If you're self-employed, an S-Corp owner, or a partner in a partnership, the IRS expects you to pay tax as you earn income. That's what quarterly estimated payments are for. Plan them properly and you eliminate the April surprise, cut penalties, and keep control of your cash flow. Here's how they work and how to stay ahead.

For the upcoming installment, use our September 15, 2026 cash-planning checklist to connect the confirmed payment with available funds and upcoming commitments.

Why Estimated Taxes Matter

Employees have tax withheld from every paycheck. Most business owners don't — you're responsible for paying your own income tax and self-employment tax throughout the year, in four installments.

Underpay and you can owe an underpayment penalty (IRC §6654) even if you pay the full balance when you file. The penalty depends on the underpaid amount and how long it remains unpaid, calculated separately for each payment period under the applicable IRS rules. For contractors, whose income swings month to month, it's easy to spend money that should have gone to the IRS.

Who Has to Pay

You generally owe estimated payments if you expect to owe $1,000 or more in tax at filing after subtracting withholding and credits (IRC §6654(e)). That typically covers:

• Sole proprietors
• Partners in partnerships
• S-Corp shareholders
• Self-employed individuals
• Anyone with meaningful income not subject to withholding

Even if you take a reasonable S-Corp salary with withholding, you may still owe estimates on pass-through taxable income and other income, even when no cash is distributed — a gap that catches a lot of owners.

The Four Deadlines

For a calendar-year taxpayer, estimated payments are due:

• Q1 — April 15
• Q2 — June 15
• Q3 — September 15
• Q4 — January 15 of the following year

If a due date lands on a weekend or holiday, it moves to the next business day. Our tax due dates page tracks the current-year deadlines.

How to Calculate What You Owe

There are two main approaches.

1. Safe harbor (simplest for most owners)

The IRS safe harbor (IRC §6654(d)) shields you from an underpayment penalty as long as your timely payments hit one of these marks:

• 100% of last year's total tax — or 110% if your prior-year adjusted gross income was over $150,000 ($75,000 if married filing separately); or
• 90% of this year's actual tax.

Many contractors use the "100% (or 110%) of last year's tax" route because it's a known, fixed number: take last year's total tax, divide by four, pay that each quarter. You're penalty-protected even if you end up earning — and owing — far more this year. You still settle the difference at filing, but without the penalty.

2. Annualized income installment method

If your income is lumpy — normal for contractors — the annualized income installment method (IRC §6654(d)(2)) lets you pay less in slow quarters and more in strong ones, matching payments to when you actually earn. It's more calculation, but it prevents overpaying early in a front-loaded safe-harbor schedule.

Common Mistakes That Cause the April Surprise

• Not setting money aside as it comes in — treating all revenue as spendable cash is the single biggest cause.
• Ignoring the safe harbor — miss it and you can be penalized even after paying in full.
• Forgetting pass-through income — salary withholding may not cover the tax on your share of business income, whether or not it is distributed.
• Waiting until year-end to check — by then it's too late to fix the current year's payments.
• Not updating estimates when income jumps — a strong second half leaves you underpaid if the later payments don't rise.

Practical Tips for Contractors

• Open a separate tax savings account. Move a fixed percentage of every payment you receive into it, so the money is already set aside.
• Review quarterly. Sit down with your accountant (or your books) before each due date and adjust.
• Use the safe harbor when you can. It's the cleanest penalty protection.
• Coordinate salary and distributions. If you run an S-Corp, make sure your reasonable salary carries proper withholding and your distributions are built into the estimate.
• Keep books current. Real-time income and expense tracking makes accurate estimates far easier.

Stop the April Surprise

A large April bill with penalties is stressful and, for most owners, completely unnecessary. A simple quarterly system eliminates the surprise, cuts penalties, and puts you back in control of your cash. If you've been guessing at your payments — or been caught off guard before — now's the time to fix the process. Contact KDM Accounting Services and we'll set the right amounts, build a practical system, and keep you on track all year.

For the complete eligibility conditions and installment calculations, see IRS Publication 505. The prior-year safe harbor generally requires a prior return covering a full 12-month year. Meeting an annual target late does not automatically resolve an earlier installment shortfall.