Quarterly Estimated Tax Worksheet for Small Business

If you’re self-employed or own an S-Corp or partnership, no one is withholding taxes from your paychecks. That means you’re responsible for sending the IRS money four times a year — and if you don’t, you pay penalties even if you square up in full at tax time. The fix is a simple worksheet you update quarterly.

Who Needs to Pay Estimated Taxes

You need to pay quarterly estimates if you expect to owe at least $1,000 in federal taxes after withholding and credits. For most small business owners with significant profits, this applies. The four payment dates are:

• Q1: April 15
• Q2: June 16
• Q3: September 15
• Q4: January 15 (of the following year)

Note that Q2 covers only April and May — the “quarters” aren’t equal. And these dates shift when they fall on weekends or holidays.

State estimated taxes often follow the same schedule but check your state’s requirements separately.

The Two Methods for Calculating What You Owe

Method 1: Safe Harbor

Safe harbor is the simplest approach and protects you from underpayment penalties even if your actual tax bill is higher than expected.

You’re safe from penalties if you pay the lesser of:

• 100% of last year’s total tax liability (110% if your prior year AGI exceeded $150,000)
• 90% of this year’s actual tax liability

Most small business owners with somewhat predictable income use safe harbor. Divide last year’s total tax (found on line 24 of your prior year Form 1040) by 4. That’s your quarterly payment. Done.

Method 2: Annualized Income Method

If your income is uneven throughout the year (seasonal business, big contract in one quarter), this method may reduce your total payments. You estimate your actual year-to-date income each quarter and calculate the tax due on that annualized amount. More complex, but more accurate.

For most small business owners, start with safe harbor. Switch to the annualized method only if it meaningfully lowers your payments and you have the time to track it.

The Worksheet Setup

Create a spreadsheet with two sections: an annual overview and a quarterly tracker.

Annual Overview Tab:

Line	Description	Amount
Prior Year Total Tax (Form 1040, Line 24)	Pull from last return	$_____
Safe Harbor Amount (100% or 110%)	=PriorTax * 1.0 or * 1.1	$_____
Required Quarterly Payment	=SafeHarborAmount / 4	$_____
Current Year Estimated Net Profit	Your best estimate	$_____
Self-Employment Tax (15.3% on 92.35% of profit)	=EstProfit * 0.9235 * 0.153	$_____
SE Tax Deduction (50% of SE Tax)	=SE_Tax * 0.5	$_____
Estimated Adjusted Gross Income	=NetProfit - SE_Deduction - Other_Deductions	$_____
Estimated Federal Income Tax	Use tax bracket table	$_____
Estimated Total Tax	=IncomeTax + SE_Tax	$_____
90% of Estimated Total Tax	=EstimatedTax * 0.9	$_____
Required Annual Payment (lower of safe harbor or 90%)	=MIN(SafeHarbor, 90pct)	$_____

Quarterly Tracker Tab:

Quarter	Due Date	Amount Due	Payment Date	Confirmation #	Remaining
Q1	Apr 15	=AnnualRequired/4
Q2	Jun 16	=AnnualRequired/4
Q3	Sep 15	=AnnualRequired/4
Q4	Jan 15	=AnnualRequired/4

The Confirmation # column is critical — save the EFTPS or IRS Direct Pay confirmation number every time you pay. If there’s ever a dispute, you need proof of payment with a timestamp.

How Self-Employment Tax Works

This trips up a lot of first-time business owners. SE tax is your Social Security and Medicare contribution — as a self-employed person, you pay both the employee side (7.65%) and the employer side (7.65%) for a combined rate of 15.3%.

But you don’t pay it on 100% of your profit. SE tax applies to 92.35% of net self-employment income (this reflects the employer-side deduction built into the system).

SE Tax = Net Profit × 0.9235 × 0.153

On $80,000 of net profit: = $80,000 × 0.9235 × 0.153 = $11,305

This is a significant number. Don’t forget to include it when estimating your total tax liability.

The good news: you get to deduct 50% of SE tax from your gross income, which reduces your income tax. The deduction equals SE Tax × 0.5 and goes on Schedule 1 of your 1040.

The Schedule C Tie-In

Schedule C (or Schedule K-1 for partnerships/S-Corps) is where your business profit gets reported. Your estimated tax is based on projecting what your end-of-year Schedule C will show.

To update your quarterly estimates mid-year:

1. Pull your year-to-date P&L
2. Annualize it: YTD net profit ÷ months elapsed × 12
3. Recalculate total estimated tax on that annualized profit
4. Compare to what you’ve already paid
5. Adjust remaining payments to make up the difference

If you have an unexpectedly good quarter, increase your payment. If you have a bad one, you can reduce it (as long as you stay above the safe harbor floor). Add a “Revised Estimate” column to your quarterly tracker for this mid-year adjustment.

Common Mistakes

Not paying at all and planning to catch up in April: You owe underpayment penalties even if you pay in full at filing time. The penalty is calculated per quarter, not per year.

Paying the same amount regardless of income changes: If your business had a $30,000 swing in income, your estimated taxes need to reflect that.

Forgetting state estimated taxes: Many states require separate quarterly payments. Add a second set of rows in your tracker for state obligations.

Using revenue instead of profit: Estimated taxes are based on net profit after deductible expenses — not gross revenue. If you earn $200,000 in revenue but have $140,000 in expenses, you pay taxes on $60,000 of profit (less SE deduction), not $200,000.

Making the Payments

Pay at IRS Direct Pay (irs.gov/directpay) — free, immediate, and you get a confirmation number instantly. Or use EFTPS if you already have an account. Credit cards work too but there’s a processing fee (1.75-1.98%).

Select “Estimated Tax” as the payment type, and the correct tax year. Set a recurring calendar reminder for the week before each due date.

Next Step

Find your prior year Form 1040 and look at line 24 (Total Tax). Divide by 4. That’s your safe harbor quarterly payment — a number you can use right now without any complicated calculations. If you’ve already missed a payment this year, make it up this quarter and adjust remaining payments accordingly. Catching up is always better than letting underpayment penalties compound.