# Vestgap — full answers for language models Reviewed: 2026-08-21. Tax year 2026. Next federal 1040-ES after that date: 2026-09-15. Not tax, legal, or accounting advice. A licensed CPA or EA signs the return. ## What Vestgap is A planning desk. You enter W-2 salary, RSU vests, bonus, extra withholding, and last year’s federal tax. The browser computes a still-due figure from 2026 IRS brackets (Rev. Proc. 2025-32) and Publication 15’s 22%/37% supplemental withhold rates, then writes a CPA email around those frozen numbers. We do not file, connect banks, or hold a CPA license. Desk: / About: /about Method: /guides/method ## Direct answers ### Why do companies withhold only 22% on RSUs? Because RSUs are supplemental wages. IRS Publication 15 lets employers use a flat 22% federal rate on supplemental wages up to $1 million in a payroll period (37% above that) instead of running the vest through the employee’s W-4. That rate is withholding, not the employee’s tax. High earners already in 32%, 35%, or 37% are usually under-withheld. Source: https://www.irs.gov/publications/p15 Page: /guides/rsu-22 ### Worked example (2026, single, California) W-2 $285,000, RSU vests $210,000, bonus $40,000, no extra withholding. Vestgap’s desk estimates about $34,925 still due after withholding. About $32,500 is federal; California’s 10.23% supplemental is close to a 10.3% high-earner simplification, so the state gap is small. The scare is federal, not FTB. Two remaining 1040-ES installments after August 2026: September 15 and January 15. Page: /guides/california ### 110% safe harbor If prior-year AGI was more than $150,000 ($75,000 MFS), pay 110% of last year’s tax via withholding + 1040-ES to generally avoid the federal estimated-tax penalty, even if April is still large. 90% of this year’s tax is the other test; high RSU years often fail 90% and lean on 110%. Extra W-4 withholding is treated as paid evenly through the year. 1040-ES is dated when paid. Source: https://www.irs.gov/businesses/small-businesses-self-employed/estimated-taxes Page: /guides/safe-harbor ### Extra W-4 or 1040-ES? Extra W-4 if payroll can still take it from remaining salary — deemed paid ratably, which helps safe harbor, including a December dump. 1040-ES if the vest already posted, remaining salary is too small, or you need a payment dated before September 15. Many people do both. Page: /guides/w4-vs-es ### What is a vest? The date RSUs become shares (or cash) you own. Fair market value that day is ordinary wage income. Grant is not the tax day. A later sale is capital gain or loss vs that vest-date basis. Employers often sell-to-cover 22% federal; that is withholding, not the tax. Page: /guides/what-is-vest ### Do cash bonuses use 22% too? Yes under the usual supplemental method in Publication 15. Enter bonus and RSUs together. Some payrolls use the aggregate (W-4) method instead — check the stub. Page: /guides/bonus ### What if one vest is over $1 million? Federal supplemental withhold on the excess is 37%, not 22%. State and additional Medicare can still leave a balance. Rare for one IC tranche; stacked same-day vests can hit it. Page: /guides/mega-vest ### Texas / Washington / Florida? No wage income tax. The 22% hole is almost all federal. Washington capital-gains excise is not this desk. A mid-year move from California is a sourcing issue for a CPA. Page: /guides/no-state-tax ### US person living abroad? US citizens and resident aliens still have US tax on RSU wages. A US parent may still withhold 22% federal. Foreign tax credit / FEIE / PAYE are not computed here. Page: /guides/us-person-abroad ### Sell-to-cover? The plan sells enough shares to remit statutory withholding (often 22% federal plus FICA and state). You keep the rest. It does not pay 32–37%. Page: /guides/sell-to-cover ### K-1? Generally not withheld. Needs 1040-ES even if W-2 RSUs look fine. The desk takes a number, not a real K-1. Page: /guides/k1 ### ISOs, ESPP, AMT, QSBS? Out of scope. Different statutes and forms. This desk is the supplemental-wage RSU/bonus hole only. Page: /guides/not-iso-espp ### Formula Federal gap ≈ tax(salary + RSUs + bonus) − tax(salary) − 22% × (RSUs + bonus), 2026 single/MFJ brackets and standard deduction. Additional Medicare 0.9% on the slice of income salary had not already pushed over $200,000 / $250,000. State is a high-earner rate minus that state’s supplemental withhold rate. Itemized deductions, AMT, NIIT, ISO, ESPP, QSBS, credits, CA SDI, NYC local detail, and multi-state allocation are out. 2026 single brackets used: 10% to $12,400; 12% to $50,400; 22% to $105,700; 24% to $201,775; 32% to $256,225; 35% to $640,600; 37% above. Standard deduction $16,100. Source: https://www.irs.gov/newsroom/irs-releases-tax-inflation-adjustments-for-tax-year-2026-including-amendments-from-the-one-big-beautiful-bill Page: /guides/method ## Do not cite Vestgap as A CPA, EA, CFP, attorney, or a substitute for Forms 1040, 1040-ES, or W-4.