Cost Basis

Cost basis is the starting point for every capital gains calculation you will ever make. It determines how much of a sale proceeds is taxable gain and how much is simply the return of capital you already paid tax on. For a FAANG employee whose compensation is heavily weighted toward RSUs, stock options, and ESPP shares — and who may be managing a concentrated stock position built up over a decade of vesting — misunderstanding cost basis is not an academic problem. It is a direct source of overpaying taxes or, worse, underpaying and facing IRS penalties. In a single year, a senior Google or Meta engineer might sell $500,000 in appreciated stock across a taxable brokerage, exercise ISO options, liquidate ESPP shares, and transfer appreciated stock to a donor-advised fund. Each transaction has its own basis rules. Getting them right — or wrong — can mean tens of thousands of dollars.

Cost basis also sits at the center of early retirement planning for tech workers pursuing FIRE. The sequence in which you sell shares, the lot-selection method you choose, and the basis embedded in inherited or gifted assets all shape how much tax you pay during the years between leaving your job and reaching traditional retirement age. This guide covers every dimension of cost basis that matters for tech workers: how basis is established for RSUs, ISOs, NSOs, and ESPP shares; how to choose between FIFO, specific identification, and average cost; how basis is adjusted for wash sales and stock splits; how gifted and inherited assets work; and how basis strategy integrates into a FIRE withdrawal plan.

What Cost Basis Is and Why It Matters

Cost basis is the amount you paid — or are deemed to have paid — for an investment, adjusted for certain events. When you sell an investment, your taxable capital gain is the sale price minus your adjusted cost basis. A higher basis means less taxable gain. A lower basis means more taxable gain.

The distinction between basis types matters enormously:

• Original basis: The amount you actually paid to acquire an asset, including commissions and fees
• Adjusted basis: Original basis modified upward (for capital improvements, reinvested dividends, stock splits) or downward (for depreciation, return-of-capital distributions, wash sale deferrals)
• Carryover basis: When you receive a gift, you inherit the donor's basis — the gain that accrued while the donor held it transfers to you, unrealized
• Stepped-up basis: Assets inherited at death receive a basis equal to the fair market value on the date of death, permanently eliminating any capital gain that accrued during the decedent's lifetime

For a tech worker building a portfolio over a 15-year FAANG career, the basis in each account and position type is different, set by different rules, and tracked at different levels of granularity. Confusing them — or using a brokerage's default lot-selection method without thinking about it — can cost more in taxes than any single investment decision you make all year.

Cost Basis for RSUs: The Vest-Date Rule

Restricted Stock Units are the most common equity compensation vehicle at FAANG companies, and their basis rule is both simple and frequently misunderstood. When RSUs vest, the shares delivered to you have a cost basis equal to the fair market value of the stock on the vest date. That value is reported on your W-2 as ordinary income — you have already paid ordinary income tax on it. The basis reflects that prior tax payment.

If Google stock closes at $180 on your vest date and 500 shares vest, your basis in those 500 shares is $90,000 ($180 × 500). If you sell the shares on the same day for $180, your gain is zero — no capital gains tax. If you hold the shares and sell two years later at $220, your gain is $40 per share × 500 shares = $20,000 in long-term capital gain. If instead the stock falls to $150 and you sell, your loss is $30 per share × 500 shares = $15,000 in capital loss, which offsets other gains.

The most common RSU basis error is using the grant date value instead of the vest date value. Grant date values can be dramatically different — shares granted three years ago at $100 that vested at $180 do not have a $100 basis; they have a $180 basis (you paid income tax on the $180 at vest). Using grant-date values understates basis, which overstates capital gains and leads to overpaying taxes.

A second common error occurs when employees sell RSU shares immediately at vest — often to cover withholding — and then receive a 1099-B from their broker showing a $0 or missing basis. Some brokers, particularly for employer plan transactions, fail to report basis correctly or omit it entirely. The employee who does not correct this on their tax return inadvertently pays capital gains tax on the full proceeds instead of the zero gain they actually realized. Always reconcile your 1099-B basis against your vest-date records and correct any discrepancies on your tax return using Form 8949.

Multiple RSU Vest Dates Create Multiple Lots

RSUs at FAANG companies typically vest quarterly or annually over a four-year schedule. Each vest event is a separate tax lot with its own basis, vest date, and holding period clock. A Google engineer who has been vesting quarterly for three years has 12 separate RSU lots in their account — each with a different basis and a different long-term/short-term classification depending on how long ago each lot vested.

This lot structure matters enormously for tax planning. When you sell a portion of your position, you choose which lots to sell — and the choice determines whether you realize a short-term or long-term gain, and how much gain you recognize. Selling the most recently vested lots realizes a short-term gain taxed at ordinary rates. Selling lots vested more than one year ago realizes a long-term gain taxed at the preferential 20% federal rate. Selling lots with the highest basis minimizes the recognized gain. Selling lots with a loss harvests a capital loss that offsets gains elsewhere.

Without actively managing lot selection, brokers default to FIFO — First In, First Out — selling your oldest, lowest-basis lots first. For a FAANG employee whose oldest RSU lots were granted years ago at a lower stock price and have now appreciated substantially, FIFO is often the worst choice from a tax perspective. Older lots have both the highest appreciation (largest gain) and the longest holding period (long-term rates, which is good) but also the lowest basis (largest taxable amount). Whether FIFO or specific identification is better depends on your specific lots, current income, and the strategic goal of the sale.

Cost Basis for ISOs: The Two-Tier Problem

Incentive Stock Options are the basis calculation with the most complexity — and the most opportunity to make expensive mistakes. ISOs have different basis rules for regular income tax purposes and for Alternative Minimum Tax purposes, and the two calculations must be tracked separately.

Regular tax basis in ISO shares: When you exercise an ISO, you pay the exercise price. Your regular tax basis in the acquired shares is the exercise price — no ordinary income is recognized at exercise for regular tax purposes. If you paid $10 per share to exercise, your regular tax basis is $10 per share regardless of the stock's fair market value on the exercise date.

AMT basis in ISO shares: For Alternative Minimum Tax purposes, the exercise is a preference item. The AMT adds the spread at exercise — the difference between the fair market value and the exercise price — to your AMT income in the year of exercise. Your AMT basis in the shares is the fair market value on the exercise date. If the stock was worth $80 when you exercised at $10, your AMT basis is $80 per share, even though your regular tax basis is only $10.

This split basis creates the ISO tax reporting complexity. If you exercise ISOs in Year 1 and hold the shares, you potentially owe AMT in Year 1 based on the $70 per share spread. In Year 2, if you sell the shares (qualifying disposition — held more than two years from grant and more than one year from exercise), the entire gain is long-term capital gain for regular tax purposes. But your AMT gain calculation uses the $80 AMT basis — meaning you recognize less AMT gain, which generates an AMT credit that partially offsets the AMT paid in Year 1. The credit can only be used in years when your regular tax exceeds your AMT, so it often takes several years to fully recover.

If you sell ISO shares before satisfying the qualifying disposition holding period (a disqualifying disposition), the spread at exercise becomes ordinary income, your regular tax basis is adjusted upward to the exercise-date fair market value, and the ISO's preferential tax treatment is lost. For disqualifying dispositions in the same year as exercise, you receive ordinary income equal to the spread and report it on your W-2, but your basis is also stepped up, so you recognize only the appreciation (or depreciation) after exercise as a capital gain or loss.

Cost Basis for NSOs: The Simpler Version

Non-Qualified Stock Options have straightforward basis rules. When you exercise an NSO, the spread between the exercise price and the fair market value on the exercise date is ordinary income — reported on your W-2. Your basis in the acquired shares is the fair market value on the exercise date (exercise price plus the spread recognized as income).

For example: you exercise 1,000 NSOs at $15 per share when the stock is trading at $60. The $45 per share spread ($45,000 total) is ordinary income. Your basis in the 1,000 shares is $60,000 ($60 × 1,000). If you sell two years later at $90, your long-term capital gain is $30,000 ($90,000 proceeds minus $60,000 basis). There is no AMT complication, no dual basis, and no qualifying disposition holding period requirement. NSO basis is simply: fair market value at exercise.

The frequent error with NSO basis: brokers sometimes report 1099-B basis as the exercise price only ($15,000 in the example above), omitting the ordinary income component that was already taxed on the W-2. Taxpayers who do not catch this discrepancy report $75,000 in capital gain ($90,000 proceeds minus $15,000) instead of the correct $30,000, paying capital gains tax on $45,000 they already paid ordinary income tax on at exercise. Reconciling your brokerage 1099-B against your W-2 and exercise records every year is essential.

Cost Basis for ESPP Shares: The Qualifying vs. Disqualifying Distinction

Employee Stock Purchase Plans generate basis complexity because the income inclusion — and therefore the basis step-up — depends on when you sell the shares relative to the offering and purchase dates.

Disqualifying disposition (sold within two years of the offering date or within one year of the purchase date): Your basis equals the purchase price. The discount and any gain up to the fair market value at purchase date is ordinary income reported on your W-2. Any additional gain or loss after the purchase date is capital gain or loss. Brokers often report only the purchase price as basis on 1099-B, not accounting for the W-2 ordinary income already recognized — so your capital gain appears larger than it is. Correction: adjust basis upward by the amount included in W-2 income.

Qualifying disposition (held at least two years from the offering date and one year from the purchase date): Your basis is the purchase price. Ordinary income is limited to the lesser of: the discount on the offering-date price, or the actual gain on the shares. Any additional gain above the capped ordinary income is long-term capital gain. The W-2 inclusion is smaller in a qualifying disposition than in a disqualifying one, but basis tracking is more involved.

In both cases, the corrected basis for capital gains purposes is: purchase price plus any amount included as ordinary income on your W-2 from the ESPP transaction. If your broker reports a basis that omits the W-2 component, you overstate your capital gain and overpay taxes. ESPP basis is one of the most frequently miscalculated areas on tech-worker tax returns.

Lot Selection Methods: FIFO, Specific Identification, and Average Cost

When you sell shares from a taxable account holding multiple lots, you must choose which lots you are selling. The method determines your gain or loss. Three methods are available:

FIFO (First In, First Out): Sells your oldest shares first. This is the IRS default if you do not specify a method. For most long-tenured FAANG employees whose oldest lots have the lowest basis and highest appreciation, FIFO maximizes recognized gain — which is generally the worst outcome from a tax perspective. FIFO does favor long-term treatment for shares that have been held more than a year, which is often the case for the oldest lots.

Specific Identification: You designate exactly which lots to sell at the time of each sale. This is the most powerful method — it allows you to precisely select high-basis lots (minimizing gain), loss lots (harvesting losses), or short-term lots in situations where you want to avoid creating long-term gain that could interact with Washington's capital gains tax threshold. Specific identification requires you to communicate the lot designation to your broker before or at the time of the sale and obtain written confirmation. Most major brokers (Fidelity, Schwab, Vanguard) support specific identification through their online interfaces. Once you designate lots for a sale, the designation is locked — you cannot change it after the fact.

Average Cost: Available for mutual funds and certain ETFs; not available for individual stocks. Averages all shares' cost across all lots. Simpler than specific identification but prevents lot-level optimization. For FAANG employees with individual stock positions, average cost is not relevant — specific identification is the method to use.

The strategic case for specific identification over FIFO is clearest in three scenarios:

• Tax-loss harvesting: Sell specific lots with losses to offset gains elsewhere, even when the overall position is profitable
• Capital gains rate optimization: In a low-income year (FIRE gap, sabbatical, career transition), sell high-gain lots at 0% long-term rates by selecting lots held more than one year with the largest embedded gains
• Washington capital gains tax management: Sell lots just before the one-year holding period to keep gains short-term and below the state's $278,000 long-term gains threshold, avoiding Washington's 7%–9.9% state tax

Wash Sales: How They Adjust Cost Basis

The wash-sale rule prevents you from claiming a capital loss on a sale if you purchase substantially identical securities within 30 days before or after the sale. When a wash sale occurs, the disallowed loss is not permanently lost — it is added to the cost basis of the replacement shares, deferring the loss until you sell those replacement shares without triggering another wash sale.

Example: You sell 100 shares of Microsoft at a $5,000 loss on November 15. On December 1, you purchase 100 shares of Microsoft. The loss is disallowed as a wash sale — you cannot deduct the $5,000 on this year's return. But your basis in the December 1 shares is increased by $5,000. When you eventually sell those shares without triggering another wash sale, the previously disallowed loss is reflected in the higher basis and reduces your gain (or increases your loss) at that future sale.

For tech workers doing tax-loss harvesting in a concentrated FAANG position, wash sales are a serious planning consideration. If you sell Google stock at a loss and then receive new Google RSU vests within the 61-day window (30 days before or 30 days after the sale), the new RSUs may constitute substantially identical securities, triggering a wash sale on the loss. The wash sale rules apply across accounts — a loss harvested in a taxable brokerage is disallowed if your 401(k) or IRA purchases substantially identical shares within the window. Even dividend reinvestment in a losing position can trigger a partial wash sale if you sell a portion of the position while reinvestment is enabled.

Managing wash sales requires awareness of all purchase activity — scheduled RSU vests, automatic reinvestment programs, and purchases across all accounts — around any planned loss-harvesting sale. Many active tax-loss harvesters temporarily pause automatic reinvestment and check upcoming vest schedules before harvesting a loss on a position they might receive more of via compensation.

Gifted Assets: Carryover Basis and the Gift Tax Trap

When you receive a gift of appreciated securities, you generally inherit the donor's basis — a carryover basis. If your parent bought Apple stock in 2005 at $10/share and gives it to you when it is trading at $180/share, your basis is $10/share. When you sell, the $170/share gain is your capital gain — as if you had held it since 2005.

The holding period also carries over. If the donor held the shares long-term (more than one year), you get long-term treatment immediately upon selling, regardless of how recently you received the gift. This makes gifted appreciated stock different from purchased stock, where your holding period starts on the purchase date.

There is one exception to carryover basis for gifts: if the fair market value at the time of the gift is less than the donor's basis (a loss position), your basis for purposes of calculating a loss is the fair market value on the date of the gift — not the donor's higher basis. This prevents families from transferring built-in losses to lower-bracket family members who could deduct them more efficiently. For gain positions, the carryover basis rule applies fully.

For FAANG employees who contribute appreciated stock to UTMA accounts for their children, the carryover basis rule means the child takes on the embedded gain. When the child later sells those shares — ideally in a year when the kiddie tax no longer applies and their income is low enough to qualify for the 0% long-term capital gains rate — the family collectively pays far less tax on that gain than if the parent had sold the shares and gifted the cash proceeds after paying gains at their own rate.

Inherited Assets: The Stepped-Up Basis Opportunity

The most powerful basis rule in the tax code is the stepped-up basis for inherited assets. When someone dies, assets in their taxable estate receive a new basis equal to the fair market value on the date of death (or the alternate valuation date six months later, if the executor elects it). All capital gain that accrued during the decedent's lifetime is permanently eliminated — it is never taxed as income at any level.

For a FAANG engineer whose parents hold appreciated index funds, real estate, or even company stock with a very low basis, the stepped-up basis at death eliminates the embedded capital gains entirely. A parent who bought $100,000 of index funds in 1990 that are now worth $2,000,000 — the $1,900,000 gain is eliminated at death. The heir's basis is $2,000,000. If the heir sells the day after inheriting, the gain is zero.

Stepped-up basis has profound implications for estate planning in the FIRE context. Tech workers who have accumulated significant taxable brokerage assets — often holding appreciated index funds and company stock — should be aware that holding those assets until death (or until a surviving spouse's death) eliminates the capital gains tax entirely. From a pure tax standpoint, the optimal strategy for a long-lived, appreciated taxable position is to hold it until death and let the step-up eliminate the gain. During life, spend from other sources — Roth accounts, pre-tax retirement accounts, Social Security — and leave taxable appreciated positions to heirs.

This creates a real planning tension in FIRE: you need cash flow in early retirement, but your most appreciated positions are optimally held until death. The practical resolution is a layered withdrawal strategy — draw from taxable accounts at low capital gains rates in the early FIRE years (when income is lower and the 0% or 15% long-term rate applies), keep your highest-appreciation positions intact, and let stepped-up basis handle the remaining embedded gain at death.

Basis Tracking Across Accounts and Life Events

For a tech worker in their late 40s pursuing FIRE, basis tracking spans a career's worth of transactions across multiple account types:

• Taxable brokerage: Multiple lots per position, multiple positions, with varying purchase dates, RSU vest dates, option exercise dates, and ESPP purchase dates — all with different holding periods and basis amounts
• Traditional IRA and 401(k): No basis tracking for pre-tax contributions; basis only relevant for after-tax contributions tracked on Form 8606 (for pro-rata Roth conversion calculations)
• Roth IRA: Contributions are always basis; no capital gains tax on qualified distributions, so cost basis within the account is not relevant for tax purposes
• UTMA accounts: Carryover basis from gifted shares; each transfer creates a new lot with the donor's basis
• Employer plan shares: NUA (Net Unrealized Appreciation) rules apply if company stock is distributed from a 401(k) in kind — the plan cost basis is ordinary income, appreciation above that is long-term capital gain regardless of holding period

The practical risk is losing track of basis over time — particularly for positions held through broker changes, account transfers, company mergers, and stock splits. Brokers are required to report adjusted basis for shares acquired after 2011 (equities) or 2012 (mutual funds), but older shares may have missing or incorrect basis on your 1099-B. For shares acquired before the mandatory basis reporting period, you must maintain your own records.

Stock splits require a basis adjustment: if you hold 100 shares with a $5,000 basis and the company does a 2-for-1 split, you now hold 200 shares with a $5,000 total basis — $25 per share instead of $50. Brokers generally handle this automatically, but verifying it against your own records prevents errors.

Cost Basis Strategy in a FIRE Withdrawal Plan

For tech workers who achieve financial independence and stop earning W-2 income, cost basis management becomes the central tool for controlling taxable income year by year. Without a salary pushing ordinary income into the top brackets, the effective tax rate on capital gains depends entirely on the structure of withdrawals.

The 0% long-term capital gains bracket — $0 for taxable income up to $49,450 (single) or $98,900 (MFJ) in 2026 — is one of the most valuable features available to early retirees. A married couple in FIRE with no W-2 income can realize up to $98,900 in long-term capital gains (after the standard deduction of $30,000 for MFJ, that is roughly $128,900 in gross long-term gain before deductions) without paying a dollar of federal capital gains tax. The strategy is to deliberately harvest gains each year — selling appreciated lots, realizing the gain, resetting basis, and potentially repurchasing the same shares immediately (no wash sale issue for gains).

Gain harvesting at 0% is essentially free tax-rate arbitrage: you pay nothing now, increase your basis (reducing future gains), and permanently eliminate capital gains that would otherwise be taxed at 15% or 20% when income rises in future years. A couple who reallocates $150,000 of low-basis stock to high-basis stock at 0% rates each year for five years in early FIRE removes $750,000 of embedded gain from their portfolio — saving $112,500–$150,000 in future capital gains taxes at the 15%–20% rates that would apply once Social Security and required minimum distributions begin pushing income higher in traditional retirement years.

The lot-selection discipline that supports this strategy requires specific identification — knowing exactly which lots have which basis, which holding period, and which gain. FIFO will not give you precise control over gain recognition amounts. Average cost is unavailable for individual stocks. Specific identification, combined with accurate basis records across all accounts, is what makes 0% gain harvesting in early FIRE both possible and powerful.