One of the most common surprises for first-year business owners: a large April tax bill plus a penalty for not paying throughout the year. If you came from W-2 employment, nothing in that experience prepared you for this.
Here's how quarterly estimated taxes actually work — and how to make sure you're not overpaying or underpaying.
Why Quarterly Payments Exist
The U.S. tax system is pay-as-you-go. When you're an employee, your employer withholds tax from every paycheck and sends it to the IRS on your behalf. You don't have to think about it.
When you're self-employed, a business owner, or a freelancer, there's no employer handling that withholding. You're responsible for paying your tax liability throughout the year yourself. Quarterly estimated payments are how you do that.
If you don't make them — or don't make them in sufficient amounts — the IRS charges an underpayment penalty. It's essentially interest on the amount you should have paid and didn't. The current rate is the federal short-term rate plus 3 percent, calculated on the underpaid amount for each quarter.
Who Has to Make Quarterly Payments
You're required to make estimated tax payments if you expect to owe at least $1,000 in federal taxes for the year after subtracting any withholding and credits.
This applies to: sole proprietors, freelancers and independent contractors, partners in a partnership, S-Corp shareholders who receive distributions, landlords with rental income, and anyone with significant investment income.
If you also have a W-2 job, you can sometimes cover your estimated tax liability by increasing your withholding from your paycheck rather than making separate quarterly payments. This is simpler when it works.
Guessing at quarterly payments leads to penalties or cash tied up for nothing. Let us calculate what you should actually be sending.
The Due Dates
The quarterly due dates don't divide the year evenly — a fact that confuses a lot of people.
- Q1 (January–March): payment due April 15
- Q2 (April–May): payment due June 15, 2026
- Q3 (June–August): payment due September 15
- Q4 (September–December): payment due January 15 of the following year
Q2 only covers two months, not three. The IRS hasn't explained this particularly clearly — it's just how the schedule works.
How to Calculate What You Owe
There are two methods to calculate quarterly payments, and either one protects you from the underpayment penalty.
Method 1: The safe harbor method. Pay 100 percent of your prior year tax liability in four equal installments. If your adjusted gross income in the prior year exceeded $150,000, pay 110 percent of your prior year liability.
This method is simple. You don't need to estimate your current year income at all. As long as you pay enough to meet the prior-year threshold, you're protected from the underpayment penalty regardless of what you actually owe this year.
The downside: if your income is significantly lower this year, you'll overpay throughout the year and get a refund — which means you gave the IRS an interest-free loan.
Method 2: Pay 90 percent of your current year tax liability. If you can reasonably estimate your current year income, you can calibrate payments to match actual liability.
This is more accurate but requires more work. You need to estimate your annual net income, project your tax liability, and recalibrate each quarter as you have more actual data.
A Simple Approach for Variable Income
For freelancers and business owners whose income fluctuates, a reliable approach is to set aside a percentage of every payment you receive. Twenty-five to thirty percent covers federal and state income tax plus self-employment tax for most people in the $50,000 to $150,000 net income range.
Keep this in a separate savings account. When quarterly payments are due, the money is already there.
Adjust the percentage based on last year's effective tax rate. If you owed 32 percent of your net income in total federal and state taxes, set aside 32 to 35 percent.
Self-Employment Tax
The quarterly payment calculation for self-employed people has to include self-employment tax — not just income tax. This is where first-year business owners often underpay.
Self-employment tax is 15.3 percent on net self-employment income up to the Social Security wage base and 2.9 percent above that. On $80,000 of net profit, that's roughly $11,304 in self-employment tax before a dollar of income tax.
When you're estimating your quarterly payments, factor in both: - Federal income tax on your projected taxable income - Self-employment tax on your projected net self-employment income
Many people estimate only the income tax piece and end up short.
State Estimated Taxes
Washington State doesn't have a personal income tax, which simplifies the situation for Washington-based business owners. (A new 9.9% tax on household income above $1 million takes effect in 2028 and faces legal challenges, but it won't affect most households.) But if you have income from other states, or if you're operating in a state with income tax, that state likely has its own estimated payment requirements with its own deadlines.
What Happens If You Underpay
If you underpay estimated taxes, the IRS calculates the underpayment penalty when you file your return. You pay it along with any remaining balance due.
The penalty isn't catastrophic — it's essentially interest at a modest rate. But it does mean you owe more than you expected, and it's entirely avoidable.
The penalty is calculated separately for each quarter. Even if you paid plenty in total, a late payment in Q2 can generate a penalty for that quarter specifically.
Adjusting Throughout the Year
You don't have to commit to one payment level for the whole year. Each quarter stands on its own.
If your income is significantly higher than expected in the first half of the year, you can increase your Q3 and Q4 payments to catch up. If you had a slow quarter, you can reduce the next payment accordingly.
Knowing what you'll owe, and when, before the bill arrives is one of the simplest things that changes how tax season feels. For our clients, calculating estimated payments is part of the ongoing relationship, not something left for tax time.