TL;DR Answer Box

RSU bonus withholding problems show up when a big year (RSUs, bonus, commissions) pushes you into higher brackets but your employer withholds at a flat supplemental rate that may be too low. In December, you can often reduce April pain by adding extra withholding on your final paychecks or making a targeted estimated payment, then pairing a spike year with tax-smart giving (including a donor-advised fund) if it fits. Finally, systematize next year’s equity sales with a rules-based 10b5-1 plan so diversification runs on autopilot.

Last updated: January 16, 2026

Introduction

Maya had a career year. Big base, multiple RSU vests, and a six-figure bonus. Then April arrived with a five-figure tax bill and underpayment penalties.

Nothing was “wrong” with her income. The problem was timing and withholding. Her RSUs and bonus stacked on top of salary, but her withholding lagged her true marginal rate.

If your income spiked in 2025, the cleanest moves usually happen in December. If you missed the December window, you still have options. You can adjust withholding for 2026 immediately, and you can coordinate any remaining 2025 catch-up steps with your CPA to reduce penalties and surprises.

Why RSUs and bonuses create tax surprises

RSUs, bonuses, and commissions are wage income. They stack on top of salary. That stacking effect is what pushes many high earners into higher marginal brackets.

The flat supplemental withholding problem

Many employers withhold supplemental wages at a flat federal rate (commonly 22%, and 37% once supplemental wages exceed $1 million). That simplifies payroll, but it can under-withhold relative to your actual marginal rate, especially in a spike year. The result is predictable: you feel “fine” all year, then taxes arrive like a surprise invoice.

Why April penalties happen

The IRS is a pay-as-you-go system. If you do not pay enough throughout the year through withholding and or estimated payments, you can owe an underpayment penalty. The painful part is that penalties are about timing, not just the total amount you pay by April.

This is why a late-year clean-up matters. You are not trying to “game” the system. You are trying to align payments with the year your income happened.

Three year-end levers to reduce April pain

Think of this as a short decision map. You are trying to cover a gap between what was withheld and what you actually owe, while using a spike year strategically if it fits your values.

• Use extra withholding when you still have payroll cycles left, or you want a simple operational fix.
• Use an estimated payment when payroll cannot realistically cover the gap.
• Use tax-smart giving when you already give (or want to start) and the timing supports a larger deduction in a spike year.

Lever 1: Fix withholding using your W-4 and extra withholding

If you have any payroll left in December, adding extra withholding can be one of the cleanest ways to close a gap. It is also operationally simple.

Here is why this lever is powerful late in the year. For estimated-tax timing purposes, withholding can be treated as paid throughout the year (rather than only when it was withheld), unless you elect to allocate it differently. That treatment can make late-year withholding especially useful for penalty prevention when your income arrived unevenly.

What to do:

1. Ask your CPA or planner to project your total 2025 tax based on your actual wage income, RSU vests, bonus, and investment activity.
2. Compare that projection to your year-to-date withholding.
3. If there is a gap, submit an updated W-4 and request additional federal and state withholding on your final paychecks or bonus.

If you want a deeper view of how bonuses and equity compensation impact taxes, start here: Tax Tips for Cash Bonuses, RSUs, and Stock Options.

Lever 2: Make an estimated payment if payroll cannot cover the gap

Sometimes the math is simple. There are not enough payroll cycles left to fix the problem, or your employer cannot implement a change fast enough.

In that case, a one-time estimated payment may reduce penalties and shrink the April surprise. Coordinate the amount with your tax professional and match the payment to the right tax year and state rules.

Important timing note: the fourth-quarter estimated payment for a prior year is typically due in mid-January. If you missed that deadline, do not panic and do not ignore it. Ask your CPA what the cleanest next step is based on your facts. In some situations, filing sooner and paying in full can reduce penalty exposure. Your options depend on your total payments, timing, and whether you qualify for any safe-harbor rules.

Lever 3: Turn generosity into a tax strategy with a donor-advised fund

If you already give, a spike-income year can be a good year to plan giving intentionally. This is not about giving for the deduction. It is about aligning giving with your values, and capturing the tax benefits that may be available when you do.

Two common approaches:

• Donate appreciated stock: You may be able to avoid capital gains on the donated shares while also claiming a charitable deduction, subject to eligibility rules and substantiation requirements.
• Use a donor-advised fund (DAF): You can potentially take a larger deduction in the current year by contributing to the DAF, then make grants to charities over time. This can be useful when income is unusually high and you want to “bunch” giving into one year.

To understand how DAFs work in a high earner context, see Donor-Advised Funds: The Tax-Smart Way to Give.

What to do with this year’s RSUs and company stock

RSUs are taxed when they vest. After vest, the decision is not “RSUs vs taxes.” The taxes already happened. The real decision is risk, liquidity, and goals.

A simple rule that reduces stress:

• If you need cash in the next 0 to 2 years: selling and de-risking into safer capital can reduce the chance you are forced to sell during a drawdown.
• If the goal is longer-term: build a rules-based plan. Do not make every vest a one-off emotional decision.

The hidden risk for executives is concentration. You can wake up and realize 30% to 60% of investable net worth is tied to one stock, one company, one industry cycle. That is not a moral failure. It is a common byproduct of career success.

Lock next year’s diversification with a rules-based 10b5-1 plan

If you want equity sales to happen without emotion and without constant “Should we sell now?” debates, a 10b5-1 plan can be the infrastructure.

Adopt when you are clean, and plan for cooling-off periods

A 10b5-1 plan needs to be adopted when you are not aware of material nonpublic information, and it may require a cooling-off period before trades can begin, especially for directors and officers. That means December planning often supports first-half execution. If you wait until you “need” the liquidity, you are usually too late.

The rules that make it work

A good plan is boring on purpose. It should answer these questions in advance:

• What is our concentration ceiling? Many executives pick a ceiling range and diversify systematically above it, but the right number depends on your full balance sheet and goals.
• What is the sales cadence? Monthly, quarterly, or tied to vest dates.
• Do we use price bands? For example, sell more above a certain price, sell less below a certain price, subject to plan design and compliance.
• Where do proceeds go? Cash for near-term goals, diversified taxable allocation for longer-term goals, and a written plan for taxes.

For a full primer, read 10b5-1 Plans for RSUs: From Legal Protection to Long-Term Diversification.

What this means for high earners

High income creates a specific type of risk. Not market risk. Process risk.

• Withholding lag: a flat supplemental rate can be too low for your real bracket.
• Decision fatigue: every vest becomes a debate, and no one wants to make the “wrong” call.
• Concentration creep: your stock exposure grows quietly until it is too large to ignore.

The fix is not more spreadsheets. The fix is a simple system: close the withholding gap, be intentional about giving if it fits, and automate equity diversification so it supports your goals instead of hijacking your attention.

If your long-term goal is optionality, the strategy is not just “save more.” It is “reduce tax drag, reduce concentration risk, and build a plan that runs when life is busy.” For the work-optional framing, see Redefining Retirement: The Hybrid Strategy That Makes Work Optional.

Common mistakes

• Assuming payroll got it right: flat supplemental withholding is not personalized.
• Waiting until April to look: April is when you learn the result, not when you can easily change it.
• Fixing taxes but ignoring concentration: taxes are one-time. Concentration can compound for years.
• Setting a 10b5-1 plan too late: cooling-off periods and company blackouts can derail your timeline.
• Using a DAF without a giving plan: a DAF can be a great tool, but it should still reflect intentional giving and proper documentation.

Action steps

Use a two-pass approach: quick clarity, then execution.

10 minutes today

1. Pull your latest paystub and note year-to-date withholding (federal and state).
2. List 2025 “stacking” items: RSU vest totals, bonus totals, commissions, and any big capital gains.
3. Pick one planning partner: your CPA or your planner. Decide who owns the projection.

60 minutes this week

1. Project 2025 tax and identify the gap (if any).
2. If December payroll remains, submit a W-4 change and request extra withholding.
3. If payroll cannot cover it, coordinate an estimated payment strategy with your CPA.
4. If you already give, decide whether a spike-year strategy (DAF or appreciated shares) fits your values and documentation capacity.

One planning block in Q1

1. Map next year’s vest schedule and blackout windows.
2. Set a concentration ceiling and define “sell rules” that you can live with.
3. Draft a 10b5-1 plan with your advisor, company counsel, and compliance team, subject to eligibility and company policy.

Key Takeaways

• Supplemental withholding can under-withhold for high earners in a spike year, so a year-end check is worth it.
• Extra withholding via W-4 can be an operationally clean way to reduce underpayment penalties late in the year.
• An estimated payment can fill the gap when payroll cannot move fast enough.
• A donor-advised fund can help bunch giving into a spike year, if giving is already part of your plan.
• A rules-based 10b5-1 plan turns equity sales into a repeatable system that supports a work-optional path.

Facts/FAQ

How do I know if my RSU bonus withholding is short for 2025?

Project your total 2025 tax with your CPA or planner, then compare it to your year-to-date withholding and any estimated payments. If there is a gap, you can often address it with extra withholding (if payroll remains) or a targeted estimated payment. Your best move depends on timing and the size of the gap.

What is the supplemental withholding rate, and why is it often not enough?

Many employers use a flat federal supplemental withholding approach on bonuses and certain equity compensation events. That flat approach can be lower than your true marginal rate in a spike year, which is why high earners can owe a large balance due in April.

Should I fix the gap with a W-4 change or an estimated payment?

It depends on timing and operational constraints. If you still have paychecks left, extra withholding can be the simplest operational fix. If payroll cannot cover the gap, a one-time estimated payment may be cleaner. Coordinate the choice with your tax professional, especially when state rules differ.

Is a donor-advised fund overkill for smaller gifts?

Not necessarily. A DAF can be useful even for five-figure giving in a spike year if you want to pull the deduction into the current year while spreading grants over time. The right answer depends on your itemization, the charities you support, and your documentation habits.

When should I implement a 10b5-1 plan?

When you are “clean” and well before you want trades to start. Many plans require a cooling-off period and must comply with company trading windows, so December planning often supports first-half execution. Your company’s policy and your role (officer or director status) matter.

How much company stock is too much?

There is no universal number. Many executives set a single-stock ceiling range and diversify systematically above it, but your ideal ceiling depends on your cash reserves, job stability, spending needs, and total balance sheet. If one stock can derail your near-term goals, it is probably too much.

How does this tie into a work-optional goal?

Lower tax drag and automated diversification can increase optionality by reducing surprises and protecting progress. The bigger win is that your equity strategy becomes a system that supports your timeline, instead of a recurring stressor that steals attention.

Internal Links

• Tax Tips for Cash Bonuses, RSUs, and Stock Options: Deeper context on how variable comp impacts taxes.
• Donor-Advised Funds: The Tax-Smart Way to Give: How to use a DAF in a high-income year.
• 10b5-1 Plans for RSUs: From Legal Protection to Long-Term Diversification: A practical 10b5-1 playbook.
• Redefining Retirement: The Hybrid Strategy That Makes Work Optional: The work-optional framework this strategy supports.
• How to Grow Your Wealth, Not Your Tax Bill: Broader strategies to reduce lifetime tax drag.

External Links

• IRS Publication 15 (Circular E): Employer withholding on supplemental wages
• IRS Publication 505: Tax withholding and estimated tax
• SEC fact sheet: Rule 10b5-1 updates and cooling-off periods

CTA

If 2025 was a spike-income year, you do not need a complex tax model to take the next right step. You need clarity on the gap, a clean withholding or payment fix, and a rules-based plan for equity sales that reduces concentration and stress.

Book a Wealth Clarity conversation. We will map your actual 2025 income (including RSUs and bonus timing), patch withholding or estimated payments, right-size giving if it fits, and draft a 10b5-1 equity playbook designed to support a work-optional path.

Disclaimer

This content is for educational purposes only and is not tax, legal, or investment advice. Rules and eligibility depend on your facts and your company plan and policy, so coordinate decisions with your CPA, attorney, and financial professional.