1. Who Needs to Pay Quarterly

Anyone who expects to owe at least $1,000 in tax after withholding and credits — including most business owners, real estate investors, and high earners with significant investment or self-employment income — is generally required to make quarterly estimated payments.

2. The Safe Harbor Rules

Underpayment penalties are avoided entirely if total payments equal at least 90% of the current year's actual tax liability, or 100% of the prior year's liability. That prior-year figure rises to 110% for higher-income taxpayers, meaning those whose 2025 adjusted gross income exceeded $150,000, or $75,000 if married filing separately.
You use whichever of those options produces the smaller required payment. For most business owners and investors with variable income, the prior-year safe harbor is both easier to calculate and safer to rely on than forecasting the current year accurately. One narrow exception: if at least two thirds of gross income comes from farming or fishing, the current-year percentage is 66 and two thirds percent rather than 90%.

3. Quarterly Due Dates

For a calendar-year individual, the 2026 estimated tax payments are due on:

Notice that these are not evenly spaced. The gap between the first and second payment is two months, the gap between the third and fourth is four months. Business owners who assume a clean three-month rhythm routinely miss the June deadline.
A fiscal-year taxpayer uses the 15th day of the fourth, sixth, and ninth months of the fiscal year, plus the first month after year end.

4. Worked Example

A real estate investor with highly variable income from property sales pays based on 110% of the prior year's tax liability (since their prior-year AGI exceeded $150,000), spreading that amount evenly across the four due dates. Even though current-year income ends up much higher due to a large property sale, no penalty applies because the safe harbor was met — the additional tax is simply due with the return, not subject to underpayment penalties.

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5. Safe Harbor vs. Underpayment: A Comparison
 

6. Why Variable-Income Owners Get This Wrong

Real estate investors and business owners with lumpy income — a big property sale, a bonus year, a one-time consulting contract — often base estimated payments on a rough guess rather than either the safe harbor calculation or a true quarterly projection, which is exactly the situation where penalties show up at filing time.

7. Checklist

• Calculate prior-year tax liability and confirm whether the 100% or 110% safe harbor threshold applies
• Compare safe harbor payment amount to a current-year projection, and use whichever is lower
• Mark all four due dates on the calendar (they are not evenly spaced)
• Adjust projections mid-year if a major income event occurs (property sale, bonus, etc.)
• Confirm state estimated tax requirements separately, as state due dates and safe harbor rules can differ

8. Most Common Mistakes

Assuming the periods are three months apart. The actual due dates are unevenly spaced, and missing this assumption is a common cause of late payments.

Guessing instead of using the safe harbor. The safe harbor calculation is often simpler and safer than trying to forecast a variable-income year exactly.

Forgetting state estimated payments. State requirements and safe harbor thresholds don't always mirror federal rules.

Wondering if this strategy applies to your business? Book a free strategy call with our team

9. FAQ

What happens if I miss a quarterly payment? A penalty accrues on the underpaid amount for each period it remains unpaid, calculated similarly to an interest charge — it's not a flat fee, so the longer it's outstanding, the larger it grows.

Can I catch up if I missed Q1? Yes, though the penalty for that specific period generally still applies even if later payments make up the difference — catching up reduces but doesn't eliminate the penalty already accrued.

Do W-2 withholdings count toward my safe harbor requirement? Yes — withholding from any W-2 income is treated as paid evenly throughout the year regardless of when it was actually withheld, which can be a useful planning lever late in the year.