Amazon 5/15/40/40 RSU Vest: The Year 3 Tax Cliff
A senior engineer at Amazon walks into year 3 of her 5/15/40/40 grant with $540k of RSU income landing in one calendar year. Here is how the numbers shook out.
A senior SDE at Amazon finished her second year at the company in early 2025. Her original grant was 2,400 RSUs with the classic Amazon schedule: 5% at the end of year one, 15% at year two, then 40% at year three and 40% at year four. Years one and two paid out fine, $28k and $86k respectively at the vest-day price. Year three is different. Forty percent of 2,400 is 960 shares. At the August vest-day price near $230, that is $220,800 of supplemental wages in a single month, stacked on top of her $285k cash base and a $35k signing-bonus clawback recapture. Total W-2 wages for 2025 are going to print around $540k. She is single, lives in Bellevue, and her prior-year safe-harbor number was built for a $320k year. We ran the numbers before the August vest hit so she would know what was coming.
Situation
Her grant specifics:
- Original grant: 2,400 RSUs at 2023 join, four-year back-weighted schedule.
- Year 1 (2024): 120 shares vested at $158, $18,960 reported.
- Year 2 (early 2025): 360 shares vested at $195, $70,200 reported.
- Year 3 (August 2025): 960 shares vesting at projected $230, $220,800 expected.
- Year 4 (August 2026): 960 shares at unknown price.
Cash compensation was $285,000 base plus a sign-on second-year recapture of $35,000 that showed up on her 2025 W-2 as additional wages. Her 2024 federal tax bill was $71,400. She paid it through payroll withholding and a modest Q4 estimated payment. Under IRC §6654, her safe harbor for 2025 is the greater of 90% of current-year tax or 110% of last year (since 2024 AGI exceeded $150k). She needs to pay in $78,540 to avoid underpayment penalties, and Amazon’s default supplemental withholding is going to leave her short.
Washington has no state income tax, which simplifies the state side. But the federal picture is ugly. At $540k of wages, she sits squarely in the 35% federal bracket, with the top $14k in the 37% zone. Amazon withholds supplemental wages at 22% up to the first $1M, then 37% above. Her 2025 supplemental income from RSUs and the clawback is roughly $256k. All of it gets 22% withheld. Her marginal bracket on that money is 35%. That is a 13-point gap, or about $33,300 of under-withholding on RSUs alone.
What we modeled
We built three scenarios. Table numbers are 2025 dollars, federal only.
| Option | Q4 estimated payment | Year-end tax bill | Safe-harbor status |
|---|---|---|---|
| Do nothing, pay at filing | $0 | $51,200 owed April 15 | Fails safe harbor, ~$2,100 penalty |
| Q4 estimated payment of $45k | $45,000 | $6,200 owed April 15 | Passes safe harbor |
| Sell-to-cover extra at RSU vest (request 35% SWS on supplemental through Fidelity) | $0 | $8,900 owed April 15 | Passes safe harbor |
Amazon’s equity platform does not let employees request a custom supplemental rate, so option 3 required a workaround. She increased her W-4 Step 4(c) additional withholding by $6,000 per paycheck for the four paychecks following the August vest. That pulled an extra $24,000 into regular wage withholding at her marginal rate, rather than trying to fix it at the supplemental-rate level. She supplemented that with a $22,000 Q4 estimated payment on January 15.
What she did
She ran option 3 with a modified W-4, plus a $22k January 15 estimated payment. Total extra federal withholding pulled in: $46,000. Her April 15 bill landed at $7,800, well inside safe harbor, and the underpayment calculation came out clean because the W-4 withholding is treated as evenly paid across the year under IRC §6654(g).
The W-4 approach mattered. Estimated payments under §6654 are credited when paid, so a big Q4 payment does not cure Q1, Q2, or Q3 shortfalls. Withholding through W-4 is deemed paid ratably over the year by default, which means she could effectively backdate the catch-up.
What she wishes she had done differently
Two things. First, she did not diversify the year-2 or year-3 vest proceeds until November. Amazon stock dropped 8% between August and November 2025. On 676 net-of-tax shares from the August vest, that cost her about $12,400 of after-tax value. Holding vested RSUs is functionally identical to buying the same dollar amount of company stock with cash, and she would never have taken $140k of cash savings and put 100% of it into her employer. The behavioral bias is that vested shares feel like “free” stock rather than cash she just earned. She should have sold at vest, reinvested into a broad-market ETF, and moved on.
Second, she underestimated how much the year-3 cliff compresses her planning window. Her 2026 year-4 vest will be another 960 shares, and if the price moves to $280, that is $268,800 more in wages. She is now going to push against the $250k Medicare surtax threshold (already past it), the $200k Additional Medicare Tax withholding trigger, and potentially the 3.8% NIIT on any investment income. Starting the 2026 planning in July 2025, not February 2026, would have let her front-load 401(k) deferrals and mega-backdoor Roth contributions before the vest hit, smoothing cash flow.
Frequently asked
Why does Amazon’s 22% supplemental withholding under-withhold so badly at my income level?
Because IRS Publication 15 allows employers to use the 22% flat supplemental rate on supplemental wages under $1M regardless of the employee’s actual bracket. If your marginal rate is 32%, 35%, or 37%, the flat rate leaves a gap equal to your marginal rate minus 22%. On $200k of supplemental income in the 35% bracket, that gap is $26,000.
Can I ask Amazon to withhold at 37% on my RSU vest?
No. The 37% rate is mandatory only on supplemental wages above $1M in a calendar year. Below that threshold, employers may use the flat 22% rate or the aggregate method, but most default to 22%. Amazon does not offer a custom rate to employees.
Is there a clean way to cover the shortfall without writing a huge April check?
Increase W-4 additional withholding (line 4(c)) through year-end. Withholding is treated as paid evenly across the year under IRC §6654(g), which solves the Q1-Q3 estimated-tax timing problem that a December estimated payment cannot fix.
Should I hold year-3 shares hoping for appreciation?
The shares are already taxed as ordinary income at vest. Holding them is a new investment decision: “would I buy this much Amazon stock today?” For most employees the honest answer is no.
Does RSU income count toward the $200k Additional Medicare Tax threshold?
Yes. RSU vest income is wages. If your wages cross $200k (single) or $250k (MFJ), the 0.9% Additional Medicare Tax applies on the excess. Amazon will withhold it automatically once you cross $200k in wages.
Composite scenario drawn from common patterns in our advisor network's casework. Names, companies, and exact numbers are illustrative. Not tax, legal, or investment advice.