Quarterly Estimated Tax Guide for Equity Compensation

Equity compensation — RSUs, ISOs, NSOs, and ESPPs — routinely creates tax obligations that exceed what your employer withholds. Whether it's the 22% supplemental withholding rate on RSUs that under-covers your 35% marginal bracket, or the zero withholding on ISO exercises that trigger AMT, the result is the same: you owe additional tax that the IRS expects you to pay throughout the year via estimated payments.

This guide is the comprehensive reference for quarterly estimated taxes as they apply to equity compensation. It covers due dates, safe harbor rules, penalty calculations, and specific guidance for each equity type.

Why Equity Compensation Creates Estimated Tax Obligations

Regular W-2 salary withholding is calibrated to your tax bracket through your W-4 form. It's imperfect, but it usually gets within a few hundred dollars of your actual liability — which is why most employees get small refunds or owe small amounts at filing.

Equity compensation breaks this system in three ways:

1. RSUs: Flat-rate under-withholding. Employers withhold 22% on RSU income regardless of your bracket. If your marginal rate is 32-37%, the shortfall is 10-15 cents on every RSU dollar.

2. ISOs: Zero withholding. When you exercise ISOs, no tax is withheld — even when the exercise triggers tens of thousands in AMT. The entire obligation falls on you.

3. NSOs: Partial withholding. NSO exercises do trigger withholding (22% supplemental), but the same under-withholding problem as RSUs applies if your marginal rate is higher.

When the total under-withholding exceeds $1,000 for the year, the IRS requires estimated payments. If you don't make them and don't meet a safe harbor exception, you'll owe an underpayment penalty.

2026 Estimated Tax Due Dates

Payment methods:

• IRS Direct Pay — free bank transfer
• EFTPS — Electronic Federal Tax Payment System (requires enrollment)
• IRS2Go app — mobile payment
• Check mailed with Form 1040-ES voucher

Quarterly Timeline: RSU Vests + Estimated Payment Deadlines

Here's how a typical RSU vesting schedule maps to estimated payment deadlines throughout the year:

Example with real numbers: If you vest $300,000 in RSUs annually and your marginal rate is 35%, the annual shortfall is approximately $300,000 × (35% - 22%) = $39,000. Spread across four quarterly payments, that's $9,750 per quarter.

Key timing insight: Notice that your February RSU vest generates income in Q1, but the first estimated payment isn't due until April 15. And a November vest only requires a January 15 payment. The IRS gives you a roughly 6-week window between earning equity income and making the estimated payment — use it to plan cash flow.

Safe Harbor Rules Explained

The IRS provides two safe harbor methods. Meeting either one protects you from underpayment penalties, even if you owe a large amount at filing:

Method 1: 90% of Current Year Tax

Your total payments (withholding + estimated payments) must equal at least 90% of your 2026 tax liability. This is hard to use in practice because you don't know your actual liability until the year ends — especially with variable equity income.

Method 2: 110% of Prior Year Tax (Recommended)

Your total payments must equal at least 110% of your 2025 total tax (Line 24 on your 2025 Form 1040). If your 2025 AGI was $150,000 or less, the threshold is 100% instead of 110%.

Why this method is better for equity compensation:

• You know the exact number from your 2025 return
• It's not affected by unpredictable 2026 equity events
• It protects you even if 2026 income spikes dramatically

Example:

• 2025 total tax: $65,000
• Safe harbor target: $65,000 x 110% = $71,500
• 2026 salary withholding (estimated): $42,000
• 2026 RSU withholding (estimated): $22,000
• Total withholding: $64,000
• Remaining to meet safe harbor: $7,500
• Quarterly estimated payment: $7,500 / 4 = $1,875

With $1,875 per quarter in estimated payments, you're protected from penalties no matter how large your 2026 tax bill turns out to be.

RSU-Specific Guidance

RSUs are the most common equity type at public tech companies, and the withholding gap is the most frequent reason employees need estimated payments.

The withholding math:

• Employer withholds 22% federal on RSU vesting
• Your actual marginal rate is likely 32-37%
• Gap: 10-15% of RSU income
• On $150,000 RSU vesting: $15,000-$22,500 federal shortfall

State withholding gaps:

• California: 10.23% supplemental vs. 9.3-13.3% actual rate
• New York: 11.70% supplemental vs. 6.85-10.9% actual rate (usually over-withholds)

Best approach for RSUs: Since RSU vesting is predictable (you know the vesting schedule), most employees are better served by adjusting their W-4 to increase salary withholding rather than making quarterly estimated payments. W-4 withholding is treated as paid evenly throughout the year, eliminating any timing concerns.

For a detailed RSU-specific walkthrough, see Estimated Taxes on RSU Income.

ISO-Specific Guidance

ISO exercises present a different challenge: there's no automatic withholding at all, and the tax trigger is AMT rather than regular income tax.

Key differences from RSUs:

• Zero withholding at exercise — the entire AMT obligation is on you
• AMT may or may not exceed regular tax (depends on exercise quantity and income)
• You can choose when and how many ISOs to exercise (unlike RSUs, which vest automatically)
• AMT generates a credit carryforward (partial recovery in future years)

When estimated payments are needed:

• You exercise ISOs with a significant spread (FMV substantially above strike price)
• The resulting AMT exceeds your regular tax
• Your salary withholding doesn't meet the prior-year safe harbor

Best approach for ISOs: Use the ISO AMT Calculator to find your AMT-free exercise limit before exercising. If you exercise above that limit, calculate the AMT and make estimated payments starting with the next quarterly deadline.

For a detailed ISO-specific walkthrough, see Estimated Tax Payments After ISO Exercise.

NSO and ESPP Guidance

Non-Qualified Stock Options (NSOs): NSO exercises are treated similarly to RSU vesting — the spread is ordinary income reported on your W-2, with 22% supplemental withholding. The same under-withholding gap applies, and the same estimated payment or W-4 strategies work.

ESPPs (Section 423): ESPP discount income is generally small relative to salary and RSU income. Most employees won't need estimated payments solely for ESPP income. However, if you're already making estimated payments for RSU or ISO shortfalls, include any expected ESPP tax in your calculation.

Underpayment Penalty Calculation

If you don't meet either safe harbor, the IRS calculates a penalty for each quarter based on:

1. Required payment per quarter — 25% of the lesser of (a) 90% of 2026 tax or (b) 110% of 2025 tax
2. Actual payment per quarter — Withholding allocated to the quarter + estimated payments made by the quarterly deadline
3. Underpayment per quarter — Required minus actual (if positive)
4. Penalty rate — Federal short-term rate + 3 percentage points, compounded daily

The penalty is calculated separately for each quarter, so catching up in Q4 doesn't eliminate penalties for Q1-Q3 underpayments.

How much is the penalty in practice? For most taxpayers, it's relatively modest — typically 8-10% annualized on the underpaid amount. On a $10,000 shortfall for one quarter, the penalty might be $200-$250. It's more nuisance than catastrophe, but it's entirely avoidable.

W-4 vs. 1040-ES: Which Approach Is Better?

Our recommendation: For employees with predictable RSU vesting schedules, W-4 adjustment is simpler and provides stronger penalty protection. For employees making strategic ISO exercises at specific times, quarterly estimated payments offer more flexibility.

You can also combine both approaches — increase your W-4 to cover the RSU shortfall, and make estimated payments for any ISO exercises you make during the year.

State Estimated Tax Requirements

State estimated taxes follow similar logic but have their own forms and, in some cases, different schedules:

California (Form 540-ES)

California requires estimated payments if you expect to owe $500+ in state tax after withholding and credits. The safe harbor rules mirror federal (110% of prior year for AGI over $150,000).

California's unique schedule:

Note Q3 is 0% — California doesn't require a September payment. This is different from the federal equal-quarter approach.

For detailed California tax information, see our California Income Tax guide.

New York (IT-2105)

New York requires estimated payments if you expect to owe $300+ in state tax. The safe harbor mirrors federal (110% of prior year). Due dates match federal quarterly deadlines.

For detailed New York tax information, see our New York Income Tax guide.

Texas and Washington

No state income tax means no state estimated payments. If you live in one of these states, you only need to worry about federal estimated taxes. For details on how zero state income tax simplifies your equity tax picture, see our Texas income tax guide and Washington income tax guide.

Putting It All Together: Annual Planning Checklist

January:

• Review prior year tax return (total tax on Line 24)
• Calculate 110% safe harbor target
• Estimate current year total income (salary + expected RSU vesting + any planned ISO exercises)
• Estimate current year withholding
• Determine if estimated payments are needed

April 15 — Q1 payment:

• Make Q1 estimated payment (or confirm W-4 is adjusted)
• Review YTD withholding on pay stubs

June 16 — Q2 payment:

• Make Q2 estimated payment
• Adjust if RSU vesting or ISO exercises have changed plans

September 15 — Q3 payment:

• Make Q3 estimated payment
• Review YTD withholding against safe harbor target
• Consider year-end ISO exercise strategy

January 15 — Q4 payment:

• Make Q4 estimated payment
• Account for any Q4 RSU vests or ISO exercises
• Prepare for tax filing (collect W-2, Forms 3921, 1099-B)

Related Resources

• 2026 Federal Tax Brackets — Complete bracket tables, standard deductions, AMT exemptions, and FICA thresholds
• Estimated Taxes on RSU Income — Deep dive into RSU withholding gaps and estimated payment calculations
• Estimated Taxes on ISO Exercise — AMT-specific estimated payment requirements after ISO exercises
• How RSUs Affect Your Tax Refund — Why RSUs turn refunds into tax bills and how to prevent the surprise
• How Equity Compensation Affects Your Tax Return — Complete guide to IRS forms and reporting for all equity types
• RSU Tax Rate — How RSU income is taxed at federal and state levels
• RSU Tax Withholding — Detailed withholding breakdown and shortfall calculations
• AMT Calculator Guide — Understanding AMT from ISO exercises
• 83(b) Election Explained — When and how to file for maximum tax savings

Calculators:

• RSU Calculator — Calculate your exact withholding shortfall
• ISO AMT Calculator — Find your AMT-free exercise limit
• 83(b) Election Calculator — Model 83(b) election tax savings
• IPO Lock-Up Calculator — Plan for IPO-related tax obligations

Frequently Asked Questions

When are quarterly estimated tax payments due? The four deadlines are April 15, June 16, September 15, and January 15 of the following year. Note the uneven quarters: Q2 covers only April-May (2 months), while Q3 covers June-August (3 months). If you file your tax return and pay the full balance by February 2, you can skip the January 15 Q4 payment.

Do I need to make estimated payments on RSU income? Only if your total withholding (salary + RSU) won't cover your tax liability and you don't meet a safe harbor. Since RSU withholding is only 22% but your marginal rate may be 32-37%, there's often a gap. However, many employees cover the gap by increasing W-4 Line 4(c) withholding instead of making estimated payments — the IRS treats paycheck withholding as evenly distributed, which provides better penalty protection. See our detailed guide on estimated taxes on RSU income.

What is the safe harbor rule for estimated taxes? You're protected from underpayment penalties if your total payments (withholding + estimated) meet either threshold: (1) 90% of your current year tax, or (2) 110% of your prior year tax (100% if prior-year AGI was $150,000 or less). The prior-year method is more practical for equity holders because you know the exact number from your previous return. If your 2025 total tax was $65,000, paying $71,500 in 2026 (110%) protects you regardless of how much equity income you earn.

Can I skip estimated payments if my employer withholds enough? Yes. If your W-2 withholding alone meets the safe harbor (110% of prior-year tax or 90% of current-year tax), no estimated payments are needed. You can increase W-4 Line 4(c) to boost salary withholding to cover the RSU shortfall — one W-4 change can eliminate the need for quarterly estimated payments entirely. See our guide on how RSUs affect your tax refund for step-by-step W-4 instructions.

What happens if I miss an estimated tax payment? The IRS charges an underpayment penalty calculated at the federal short-term rate plus 3% (approximately 8% annualized). The penalty is assessed per quarter, so catching up later doesn't eliminate penalties for earlier missed payments. On a $10,000 quarterly shortfall, the penalty is roughly $200-$250 per quarter. It's automatically calculated when you file (Form 2210). While not catastrophic, it's entirely avoidable with proper planning.