The IRS safe harbor rule helps taxpayers avoid underpayment penalties by setting minimum payment thresholds that must be met during the year. If you meet one of these thresholds through withholding, estimated payments, or both, you can generally avoid an IRS underpayment penalty, even if you still owe taxes when you file your return. At Heritage Accountants & Advisors, we apply this rule in our tax preparation services for business owners and individuals across Long Island. Here is how it works.
The safe harbor rule is an IRS provision that shields taxpayers from underpayment penalties as long as total payments during the year meet one of two thresholds.
It does not eliminate the tax you owe. It only eliminates the penalty for underpaying during the year. You can still owe a balance in April and face no penalty if the safe harbor was met.
Per IRS underpayment penalty guidance , a third threshold also applies: if the balance owed after withholding and credits is under $1,000, no penalty applies.
Pay at least 90% of your total 2026 tax liability through withholding and estimated payments during the year.
This works well when income is lower than the prior year. The risk is in estimating a moving target. If income spikes late in the year, the 90% target rises with it.
Pay 100% of the total tax shown on your prior year's full 12-month tax return, or 110% if your prior-year adjusted gross income exceeded $150,000 ($75,000 if married filing separately).
This is the simpler method for most business owners. The required amount is known from the prior year’s return, so income fluctuations during the current year do not affect it. Most Long Island business owners using cpa tax preparation services use this method because it removes the guesswork.
Safe Harbor Target Table
| Prior Year AGI | Safe Harbor Target |
|---|---|
| $150,000 or less | 100% of prior year tax |
| Over $150,000 | 110% of prior year tax |
| Married filing separately over $75,000 | 110% of prior year tax |
The IRS treats withholding more favorably than estimated payments. Withholding is considered paid evenly across all four quarters, even if withheld only late in the year. Increasing payroll withholding in Q3 or Q4 can retroactively cover earlier quarterly shortfalls.
Estimated payments only count for the quarter in which they are made. For business owners without payroll withholding, business tax preparation that accounts for quarterly timing is the most reliable way to stay inside the safe harbor.
The IRS calculates the underpayment penalty using the federal short-term interest rate plus 3 percentage points. As of 2026, that rate is approximately 7% annually for individuals, with interest accruing daily from the due date of each missed quarter. (Note: IRS interest rates are subject to change; please verify the current rate with a tax professional).
Paying everything in April does not erase a Q1 or Q2 shortfall. Each quarter stands on its own. For closely held businesses, income tax provisions experts who track quarterly positions year-round help owners catch shortfalls before they compound.
The prior year’s safe harbor is not always the right choice. Use the 90% current year method when:
The current year’s income is significantly lower than the prior year’s
A large one-time item inflated the prior year’s tax liability
The prior year return was for less than 12 months
Tax preparation services in Long Island that include mid-year income projections allow owners to model both methods and choose the lower required payment.
The Q3 estimated tax payment is due September 15, 2026. If you are unsure whether your 2026 payments are on track to meet safe harbor, now is the time to review. Heritage Accountants & Advisors provides year-round tax planning and business tax preparation services on Long Island for closely held businesses and individuals.
As a trusted CPA firm serving Nassau and Suffolk counties, Heritage Accountants & Advisors keeps your quarterly obligations on track. Call (631) 543-7700 or email info@heritage.cpa to schedule a consultation before September 15.
Disclaimer: This content is for educational purposes only and does not constitute professional tax or legal advice. Please consult with a qualified tax professional regarding your specific situation.
