Quarterly Estimated Taxes Explained for Small Business Owners

When you have an employer, taxes come out of every paycheck automatically — you never really see the money, so you never have to think about it. When you work for yourself, that system disappears. The IRS still wants to be paid throughout the year, not all at once in April, so it asks you to estimate what you’ll owe and send it in four installments. Those are quarterly estimated taxes, and this guide covers everything you need to stay on top of them.

Who has to pay quarterly estimated taxes?

The general rule: if you expect to owe $1,000 or more in tax when you file, the IRS expects quarterly estimated payments. That sweeps in most:

• Freelancers, consultants, and independent contractors (1099 income)
• Sole proprietors and single-member LLCs
• Partners and S-corp shareholders — on their K-1 share of the business’s profit, not the distributions themselves
• Anyone with significant untaxed income — rentals, investments, side gigs

Your quarterly payments cover both your income tax and your self-employment tax (Social Security and Medicare). If you’re not sure how big that combined number is, the self-employment tax estimator will give you a total and split it into four payments for you. One wrinkle for higher earners: the 12.4% Social Security half of that self-employment tax only applies up to the annual wage base (about $184,500 in 2026), so above that your combined rate isn’t strictly linear — it eases off a little.

2026 quarterly estimated tax due dates

Despite the name, the “quarters” aren’t evenly spaced three months apart. Here are the federal deadlines for the 2026 tax year:

If a due date lands on a weekend or federal holiday, it rolls to the next business day — so in some years a deadline shifts a day or two later than the 15th. Your state may have its own deadlines and payment portal.

The safe harbor rule: your penalty shield

Here’s the part that takes the stress out of estimating: you don’t have to predict your income perfectly. The IRS gives you a safe harbor. Pay at least the smaller of:

• 90% of your current-year tax, or
• 100% of last year’s total tax — bumped to 110% if your prior-year adjusted gross income was over $150,000.

Hit either target and you owe no underpayment penalty, even if you end up owing more when you file. The prior-year method is the easiest to use because last year’s number is already known: take the total tax from last year’s return, divide by four, and pay that each quarter. If this year turns out bigger, you simply settle the difference in April — penalty-free.

Example: last year’s return showed $18,000 of total tax and your AGI was under $150k. Pay $4,500 per quarter this year and you’re inside the safe harbor no matter what 2026 actually looks like.

How to pay

1. IRS Direct Pay — free bank transfer at irs.gov, no account needed. Fastest for most people.
2. EFTPS — the Electronic Federal Tax Payment System; free, lets you schedule payments in advance, but requires enrollment.
3. Form 1040-ES — the paper voucher route if you prefer to mail a check.

Whichever you choose, make the payment from the separate savings account where you’ve been stashing your tax money. Not sure how much to keep there? See how much to set aside for taxes.

What happens if you underpay

Missing or underpaying a quarter triggers an underpayment penalty that works like interest on the shortfall, accruing until you catch up. One missed quarter isn’t a disaster, but the penalty compounds, and paying extra late in the year doesn’t fully erase an earlier shortfall — the IRS looks quarter by quarter. Staying inside the safe harbor is the cleanest way to never think about penalties.

Make quarterly taxes a non-event

The hard part of estimated taxes isn’t paying — it’s knowing the number and remembering the date. Both are solvable with good bookkeeping. Cash Basis AI keeps a live tax estimate on your dashboard as your income and expenses change, tracks what you’ve already paid each quarter, and reminds you before each deadline. Instead of a frantic calculation four times a year, the number is just always there, waiting.