The Situation

Hana is 33, single, and three years into an SDE III role at Amazon's Sunnyvale office. Her total comp this year is around $410,000, and roughly $210,000 of that is stock. She is on the standard 5-15-40-40 vesting schedule, which means her year-three tranche, the big one, lands across the back half of 2026. She has been careful with money her whole adult life. She maxes her 401(k), she contributes to the ESPP, she has never carried a credit card balance, and she files her own return every April with a CPA who has never once made a mistake.

She also has about 55 percent of her net worth sitting in AMZN. Some of it is vested RSUs she never got around to selling. Some of it is ESPP stock she bought at a discount and then held, because selling felt like a decision and holding felt like no decision at all. When she came to us in July, she was not worried about taxes. She was worried about the earnings print on July 30 and what it might do to the half of her net worth she could not diversify in time.

The Gap We Found

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The taxes were the more urgent problem, and nobody had flagged it because nobody was in a position to. Amazon payroll withheld the flat 22 percent federal supplemental rate on every 2026 vest, which is exactly what payroll is supposed to do. Hana's actual federal marginal rate is 35 percent, plus the 0.9 percent additional Medicare tax on wages above $200,000. On the $121,000 of stock that had already vested by the end of July, payroll had sent the IRS about $26,600. Her real federal liability on that income was closer to $43,400. Add the Q4 tranche and the full-year federal under-withholding came to roughly $29,200. Her CPA would have caught it, in March, seven months too late to do anything but write the check and eat the penalty. And the penalty was already accruing, because Hana had never made an estimated tax payment and did not know that the third-quarter deadline was September 15.

What We Did

First we established the number she actually had to hit. Because Hana's 2025 AGI was above $150,000, her prior-year safe harbor is 110 percent of last year's tax, not 100 percent. Her 2025 total tax was $118,400, so the number to beat for 2026 is $130,240. By the September 15 deadline she needed 75 percent of that, or $97,680, paid in. Our AI agents pulled her payroll data directly and projected $86,300 withheld through mid-September, leaving a gap of about $11,400. That is the check, and now she knows the date.

Then we did something slightly counterintuitive with the rest. Rather than send four more estimated payments, we raised the extra withholding on her W-4 for the remaining pay periods of the year. Withholding is treated by the IRS as paid evenly across all four quarters, regardless of when in the year it actually happened. Estimated payments are credited to the quarter you make them in. So dialing up withholding in September and October cures the earlier quarters retroactively in a way that writing a check in September simply cannot. It is a small piece of the code, and it is worth about $1,900 to her.

One useful surprise: California was fine. The state supplemental rate of 10.23 percent slightly over-withholds against her 9.3 percent California marginal bracket. The gap was federal only, which meant we could stop looking at half the problem.

With the deadline handled, we built the diversification schedule for the tranche that has not landed yet. Shares sold at vest carry essentially zero capital gain, because the vest price is the cost basis, so the Q4 tranche gets sold on arrival and never becomes a decision she has to agonize over. For the older vested lots we are using specific lot identification to release the highest-basis shares first, spread across this year and next. Proceeds move into a direct index portfolio, which owns the individual names in the index rather than a fund, so losers can be harvested for tax losses while the overall exposure stays intact.

The Result

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• $29,200 in under-withholding identified and cured, with the $11,400 Q3 payment made before the September 15 deadline
• ~$1,900 in underpayment penalties avoided by using retroactive W-4 withholding instead of a late estimated payment
• AMZN concentration on a path from 55 percent to 26 percent of net worth over 15 months, with the largest block moving at zero capital gains
• Hana stopped watching the earnings calendar like a weather report. The Q4 tranche has a plan attached to it before it lands.

Why This Worked

Nothing here required a new product or a clever bet. It required someone looking at her payroll data, her vesting schedule, her prior-year return, and her brokerage positions at the same time, in July rather than March. Her CPA sees the return. Her brokerage sees the shares. Neither one sees the 22 percent withholding gap opening up in real time, and neither one is going to call her on August 1 about a September 15 deadline. That call is the whole job, and because Alphanso charges a flat fee rather than a percentage of her assets, making it does not depend on how much of her money we hold.

If you are on a 5-15-40-40 schedule and your year-three tranche is landing this year, the September 15 deadline is worth ten minutes of your attention. Request a callback and we will run your actual numbers.

This case study is a composite illustration based on real Alphanso client scenarios. Names and identifying details have been changed for privacy. Results are not guaranteed and will vary based on individual circumstances. All investing involves risk, including the possible loss of principal. Alphanso LLC is a registered investment adviser.