Amazon's 5/15/40/40 Back-Weighted RSU Vesting: Why Year 3 Is a Tax Problem
The Amazon vesting schedule concentrates 80% of a four-year grant into years 3 and 4. Here is what that does to supplemental withholding.
A principal engineer joined Amazon in 2023 at L7 with a total compensation package of $650,000 across year one. Base salary sat at $180,000, a sign-on bonus covered year-one equity light, and the RSU grant was 8,000 units over four years. On a standard 25/25/25/25 schedule, that would have produced $200,000 of stock vesting per year at the grant-date price of $100. The offer letter instead described a 5/15/40/40 schedule. Year one: 400 units. Year two: 1,200 units. Year three: 3,200 units. Year four: 3,200 units.
By year three the stock was at $190. Three thousand two hundred units vested. W-2 compensation from RSU settlement alone was $608,000. Combined with base salary increases and the year-three cash top-up Amazon uses to smooth the curve, Box 1 for that year crossed $850,000. The 22% supplemental withholding rate applied to the RSU income produced a shortfall of roughly $95,000 once the real marginal rate of 35% was applied to the amount above $600,000. This is not a bug. The 5/15/40/40 schedule is a deliberate retention tool. It is also a predictable tax problem.
How the Amazon schedule actually works
Amazon communicates the grant as a dollar target, not a share count. The offer letter might say “$400,000 in RSUs over four years.” That number is divided by the grant-date stock price to produce a target share count. The vesting then follows 5% at the end of year one, 15% at the end of year two, 20% every six months in year three and year four.
The cash sign-on bonuses fill the gap in years one and two. An offer letter with a $400,000 RSU target often comes with a year-one sign-on of $80,000 and a year-two sign-on of $50,000, structured so that total cash plus equity hits the intended total comp curve in years one and two. Year three is when the math assumes the stock has appreciated and the delivered equity compensation catches up.
The appreciation assumption
Amazon’s schedule presupposes that by year three, the stock will have appreciated enough to make the 40% tranche meaningfully valuable. If AMZN is flat or down, the year-three tranche is worth less than projected. If it has run, the tranche is worth substantially more than the grant-date target. Senior engineers who joined in 2020 saw year-three vests worth 2x the original dollar target. Engineers who joined in 2021 saw year-three vests worth 40% of the target.
The year-three withholding gap
The problem is that supplemental withholding under IRC §3402(g) uses a flat 22% on supplemental wage payments up to $1 million in a calendar year and 37% above that. A senior engineer whose W-2 crosses $700,000 or $800,000 in year three is firmly in the 35% federal bracket, with 3.8% NIIT on investment income, and potentially in the 37% bracket on marginal dollars. If the employee lives in California, the state rate adds 10.23% supplemental.
Work the example.
| Item | Amount |
|---|---|
| Base salary | $180,000 |
| RSU vest year three | $608,000 |
| Total W-2 | $788,000 |
| Federal tax (single, 2025 brackets, estimated) | $240,000 |
| California tax (estimated) | $80,000 |
| Federal supplemental withheld on RSU | $133,760 (22%) |
| Federal withheld on base | ~$40,000 |
| Total federal withheld | ~$174,000 |
| Federal shortfall | ~$66,000 |
The shortfall lands on April 15 of the following year. Employees who do not run this math in October typically first learn about it in March when their CPA presents a draft return.
Why the schedule concentrates retention
Back-weighting produces two forces that keep senior employees on site. The first is that leaving before year three means forfeiting the 80% of the grant that has not yet vested. The second is that the year-three tax bill is often larger than cash on hand, which means an employee who leaves the day after year-three vest is not free of Amazon: they still owe the IRS the shortfall, and they may need to sell the newly vested stock to pay it.
From a retention perspective, the back-weighted schedule works. From an employee perspective, it means every year three through five is a tax-planning year that starts in October of year two.
The refresh grant pattern
Amazon layers refresh grants on the same 5/15/40/40 schedule. A year-one refresh granted at the end of year one vests 5% in year two, 15% in year three, 40% in year four, 40% in year five. Stacking means that by year four, three separate grants are all in their back-weighted years.
| Year | Original grant | Refresh 1 | Refresh 2 | Total share vest |
|---|---|---|---|---|
| 1 | 5% | - | - | 5% of original |
| 2 | 15% | 5% | - | 15% of original + 5% of refresh 1 |
| 3 | 40% | 15% | 5% | 40% + 15% + 5% |
| 4 | 40% | 40% | 15% | 40% + 40% + 15% |
The stacking effect means that by year four or five, RSU income often exceeds base salary by a factor of three or four. Withholding planning is not optional at that stage.
What to do in October of year two
Run a projection for the coming calendar year. Include the expected year-three vest at a reasonable stock price assumption. Apply true marginal rates. Subtract supplemental withholding at 22% on the first $1M and 37% above. The difference is your estimated tax shortfall.
If the shortfall exceeds $1,000, the IRS safe harbor under IRC §6654 applies. Paying either 90% of current-year tax or 110% of prior-year tax avoids the underpayment penalty. For most Amazon senior engineers, 110% of prior-year tax is the practical benchmark because current-year numbers depend on stock price through the vesting dates.
W-4 adjustments rarely solve it
Filing a W-4 with additional withholding on base salary is one option, but the amounts required are often larger than base salary can absorb. A $66,000 shortfall divided across 26 pay periods is $2,540 per period. For an engineer whose net base pay is $4,500 per period, the additional withholding consumes a meaningful share of take-home cash flow. Estimated payments via Form 1040-ES are usually cleaner.
Sell-at-vest as the funding source
The cleanest source of cash for estimated payments is the newly vested stock itself. Sell-at-vest eliminates concentration risk and funds the tax bill from the same event that created the liability. Employees who hold everything often end up selling at worse prices later in the year to cover the April tax bill.
The year-four and year-five complications
Year four typically includes both the original grant’s final 40% and the first refresh grant’s 40% tranche. The stacking produces an income spike larger than year three. Year five often includes another stacked 40%. Each of these years requires its own projection and its own estimated payment plan.
Frequently asked
Why does Amazon use 5/15/40/40 instead of 25/25/25/25?
Retention. The economic cost of leaving before year three is substantial, which reduces voluntary turnover at the most productive stage of tenure. It also aligns equity delivery with the assumption that an engineer’s contributions compound over time.
Can I negotiate a flatter schedule?
Amazon almost never deviates from 5/15/40/40 for standard grants. Signing bonuses are the negotiable lever, not the vesting schedule. A small number of senior or external hires have negotiated flatter schedules with explicit board approval.
Does the year-three stock price matter for the grant value?
Yes. The share count was fixed at grant-date price. The value at vest is the share count times the current stock price. If AMZN rose 80% from grant to year-three vest, the year-three tranche is worth 80% more than the target.
How does this interact with the 401(k) mega backdoor?
Amazon’s mega backdoor Roth conversion is worth roughly $46,500 per year (2025 limit minus employee deferrals and employer match). Year-three vest years typically crowd out other cash-flow priorities. The mega backdoor is more accessible in years one and two when RSU income is small.
What about state tax if I move during year three?
California and New York both tax RSU income based on where the services were performed during the vesting period, not where you live on the vest date. An employee who earned the grant in California and vested it in Texas still owes California tax on the portion attributable to California workdays.
Before year three lands, run the projection in the RSU withholding gap calculator and size your Q4 estimated payment to the safe harbor.
Fourteen years working with tech employees whose RSU income pushed them into brackets their payroll systems never saw coming. Reviews VestedGrant's RSU and vesting mechanics content.
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