The third individual estimated-tax installment for 2026 is due September 15, 2026. High earners may want to review their position before that date if income, withholding, or investment activity has changed materially since the beginning of the year. RSU vesting, bonuses, business income, stock sales, and other variable income can all affect the calculation. (IRS)
What Is the September 15 Estimated-Tax Deadline?
Federal income tax generally operates on a pay-as-you-go system.
For employees, taxes are usually paid primarily through payroll withholding. Taxpayers with income that is not sufficiently covered by withholding may need to make estimated payments.
For 2026, the standard individual estimated-tax payment dates are:
- April 15, 2026
- June 15, 2026
- September 15, 2026
- January 15, 2027
The September installment generally corresponds to the payment period covering June 1 through August 31. (IRS)
Not everyone needs to make an estimated payment simply because the deadline exists.
The relevant question is whether withholding and prior estimated payments are sufficient under the taxpayer’s particular circumstances.
Who May Want to Review Estimated Taxes?
A review may be particularly useful for someone whose income does not resemble the assumptions made at the beginning of the year.
Examples include people who have:
Received a large bonus
A substantial bonus may increase taxable income faster than regular payroll withholding adjusts.
Had RSUs vest
RSU vesting generally creates taxable compensation. Depending on the withholding method and the employee’s overall income, withholding associated with the vest may or may not align with eventual federal tax liability.
Sold appreciated investments
A taxable stock sale can produce a capital gain that was not part of the original tax projection.
The IRS specifically notes that gains from asset sales can create an estimated-tax obligation. (IRS)
Earned consulting or business income
Unlike wages, independent business income may arrive without federal income-tax withholding.
Self-employment income can also create separate tax considerations.
Experienced a significant increase in income
A promotion, new position, liquidity event, or unusually profitable business year can make prior assumptions less useful.
Had household income change
A spouse returning to work, changing employers, retiring, or receiving significant variable compensation may change the household’s overall calculation.
What Is the Estimated-Tax Safe Harbor for High Earners?
One important concept is the federal safe-harbor rule.
Generally, taxpayers may avoid an estimated-tax underpayment penalty if qualifying payments during the year reach the smaller of:
- 90% of the current year’s expected tax, or
- 100% of the prior year’s tax
For certain higher-income taxpayers, the prior-year percentage increases from 100% to 110%.
For 2026, this higher-income rule generally applies when 2025 adjusted gross income exceeded $150,000, or $75,000 for married taxpayers filing separately. Special rules apply in certain circumstances, including some taxpayers with farming or fishing income. (IRS)
Safe harbor does not necessarily mean the taxpayer has paid the entire year’s eventual tax liability.
It generally addresses whether sufficient tax has been paid during the year for federal underpayment-penalty purposes.
What Should You Look at Before September 15?
A useful review may include:
- 2025 total tax
- 2025 adjusted gross income
- Expected 2026 total income
- Federal withholding year to date
- Estimated payments already made
- Bonuses received
- RSUs vested
- Investment gains and losses realized
- Business or consulting income
- Expected income for the rest of 2026
- Significant deductions or credits that have changed
A prior-year tax return alone does not show what has happened during the current year.
Likewise, a pay stub alone does not show investment or business income.
Both may be necessary to understand the full picture.
Does Uneven Income Change the Calculation?
Potentially.
Income does not always arrive evenly throughout the year.
A business owner might earn most of their profit late in the year. An executive may receive a large equity award in one quarter. An investor may realize a gain in August that did not exist in February.
The tax rules include an annualized income installment method that may be relevant when income is received unevenly.
That calculation can be more complicated than simply dividing an annual tax estimate by four, which is one reason taxpayers with lumpy income may want to consult a qualified tax professional.
What Happens If You Underpay Estimated Taxes?
The IRS may assess an underpayment penalty when insufficient tax is paid by applicable deadlines, even if the taxpayer ultimately receives a refund after filing in some situations. (IRS)
That does not mean every shortfall automatically creates a penalty.
Safe-harbor rules, withholding, timing of income, credits, and other factors can affect the result.
A September 15 Review Checklist
Before the deadline, ask:
- Has my 2026 income changed materially from 2025?
- Have I received significant income without withholding?
- Have RSUs or other equity awards vested?
- Have I realized significant investment gains?
- Is my year-to-date withholding different from what I expected?
- Have I already made estimated-tax payments?
- Do I understand which federal safe-harbor test may apply?
- Are there meaningful income events still expected before year-end?
How Does Falcon Wealth Planning Approach Tax Coordination?
Falcon Wealth Planning is a Fee-Only fiduciary Registered Investment Adviser. Our CFP® professionals and CPAs work with clients to coordinate investment management, tax planning, retirement decisions, and other financial considerations.
For households with variable compensation or investment income, tax planning may involve evaluating withholding and estimated payments alongside the broader financial plan.
Individual tax circumstances vary, and specific estimated-tax calculations should be reviewed with an appropriate tax professional.
Frequently Asked Questions
Is September 15, 2026 an estimated-tax deadline?
Yes. September 15, 2026 is the third standard estimated-tax installment deadline for calendar-year individual taxpayers.
Does everyone earning over $150,000 use the 110% rule?
Not exactly. The 110% prior-year rule generally depends on prior-year AGI exceeding $150,000, with a $75,000 threshold for married filing separately, subject to exceptions.
Does safe harbor mean I will not owe tax in April?
No. Safe harbor generally relates to avoiding an underpayment penalty. A taxpayer may still owe additional tax when filing.
Can investment gains require estimated-tax payments?
Potentially. Taxable capital gains can increase current-year tax liability and may affect the amount that should be covered through withholding or estimated payments.
Schedule a No-Cost Financial Assessment
Variable income can make tax planning more difficult to evaluate from a paycheck alone. A No-Cost Financial Assessment can help determine whether Falcon Wealth Planning’s coordinated, fee-only fiduciary approach may be appropriate for your family’s financial needs.
