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Tax-Loss Harvesting Basics

TLH Mistakes to Avoid

Pomegra Learn

TLH Mistakes to Avoid

Five common tax-loss harvesting mistakes cost investors thousands in disallowed losses and missed tax savings. Most are wash-sale violations triggered by accounts or reinvestment mechanisms the investor forgot about.

Key takeaways​

  • Wash-sale violations via spousal accounts are the #1 TLH mistake: the IRS treats married couples as a single economic unit, so loss harvests are disallowed if a spouse buys the same security within 30 days.
  • IRA contributions and withdrawals can inadvertently trigger wash-sale violations if you harvest losses in a taxable account while buying the same security in a Roth or traditional IRA.
  • Dividend reinvestment (DRIP) plans automatically repurchase shares, creating unintended wash-sale violations if not disabled during the harvest window.
  • Wash-sale adjustments cascade across multiple accounts and years, compounding errors if not tracked carefully.
  • A single harvesting mistake can take 18+ months to discover (when 1099-B arrives) and fix via amended return.

Mistake 1: Harvesting in one spouse's account while the other spouse buys​

The IRS treats married couples filing jointly as a single economic entity for tax purposes. This means the wash-sale rule applies across both spouses' accounts.

Scenario: The dangerous swap​

Year 1, January:

  • Wife harvests $40,000 loss from her taxable account by selling Apple at a loss.
  • Tax savings: $10,000 (assuming 25% bracket).

Year 1, February (unbeknownst to wife):

  • Husband, managing his own account, receives a bonus and decides to buy Apple shares for his Roth IRA.
  • Husband buys $40,000 of Apple shares in his Roth IRA.

Tax consequence:

  • IRS disallows wife's loss because husband (spouse, same household) purchased the identical security within 30 days.
  • Wife owes $10,000 additional tax, plus interest and penalties.

Why this happens​

Many couples don't coordinate investments. One spouse manages the taxable account; the other manages IRAs or a separate account. If they're not communicating about loss harvests, they might inadvertently trigger wash-sale violations.

Prevention​

  1. Coordinate before harvesting losses. Both spouses review their accounts for any planned purchases of the same security in the 30-day window.

  2. Use a household investment calendar. If wife harvests AAPL loss on Jan 15, both spouses note "AAPL—can't buy until Feb 15" on a shared calendar.

  3. Exclude spousal account from loss harvest substitution. If you harvest a loss and need to reinvest, buy a different security or buy it only in one spouse's account, not both.

Mistake 2: Harvesting losses in taxable account while buying in IRAs​

Similar issue, different accounts: Roth IRAs, traditional IRAs, and SEP-IRAs are subject to the same wash-sale rule as taxable accounts.

Scenario: The IRA contribution trap​

Year 1, December:

  • You harvest $20,000 loss from Tesla in your taxable account (sell at loss).
  • Tax savings: $5,000 at 25% rate.

Year 1, December 31:

  • You make a $7,000 Roth IRA contribution for the year and, on impulse, buy Tesla shares in the Roth (you still like Tesla long-term; you just harvested the loss).

Tax consequence:

  • Wash-sale violation. You bought Tesla in your Roth within 30 days of selling Tesla in taxable.
  • Disallowed loss: $20,000.
  • Tax owed: $5,000 + interest + penalties (roughly $5,500–$6,000 total).

Why this is tempting (and dangerous)​

After harvesting a loss, you often feel bullish on the stock again. You think, "I'll realize the tax benefit in my taxable account, then buy it back in my Roth where it can grow tax-free." Sounds smart, but it violates wash-sale rules.

Prevention​

  1. Wait 31 days before buying in any account. If you harvest a loss on Dec 15, don't buy the same security in your Roth, traditional IRA, SEP, or Solo 401(k) until Jan 15.

  2. Use a checklist. When making any portfolio purchase, check: "Did I sell this ticker in any account in the past 30 days?"

  3. Use a substitute in your IRA if you must buy immediately. If you harvested Tesla loss in taxable and want to buy automotive exposure in your Roth, buy Ford or General Motors instead of Tesla.

Mistake 3: Automatic dividend reinvestment (DRIP) triggering wash-sale​

Many brokerages default to automatic dividend reinvestment. If you harvest a loss and the company later pays a dividend, your DRIP automatically buys more shares—triggering wash-sale.

Scenario: The forgotten DRIP​

January 15:

  • You harvest a loss on Microsoft, selling all shares and realizing a $30,000 loss.
  • You reinvest proceeds in Adobe (different company).

February 22:

  • Microsoft pays a quarterly dividend ($500).
  • Your DRIP automatically purchases $500 of Microsoft shares (it's still registered as a holding in your account, even though you sold it).

March 15:

  • Your tax filing date approaches. You prepare Form 8949.
  • Only then do you notice: you bought Microsoft again in February, within 30 days of the January sale.

Tax consequence:

  • Wash-sale violation: the February dividend reinvestment triggered it.
  • Disallowed loss: $30,000.
  • Tax owed: $7,200–$11,100 (depending on bracket) plus penalties.

Prevention​

  1. Disable dividend reinvestment for harvested positions. When you harvest a loss, immediately disable DRIP for that position.

  2. Or, harvest in non-DRIP accounts. If you have a manual-reinvestment account, use it for TLH positions. Only use DRIP-enabled accounts for long-term holds.

  3. Document the DRIP status. In your spreadsheet, note: "DRIP disabled Jan 15 for 30-day wash-sale window."

  4. Review account settings monthly. Some brokerages reset DRIP settings during system upgrades. Check quarterly.

Mistake 4: Misunderstanding the 30-day window​

The wash-sale rule is 30 days before and 30 days after the sale. Many investors only count forward, forgetting the backward window.

Scenario: The look-back miss​

November 20:

  • You harvest a loss from General Electric (GE), selling all shares.

October 25 (20 days before the Nov 20 sale):

  • You purchased additional GE shares (you didn't realize this is within 30 days of a future sale).

Tax consequence:

  • The October purchase is within 30 days before the November sale.
  • Wash-sale rules apply: The loss on the November sale is disallowed, and the disallowed loss is added to the cost basis of the October shares.

This is surprising because you didn't "buy back" the stock—you bought it before you sold it. But wash-sale looks at the entire 60-day window (30 before + 30 after).

Prevention​

  1. Check your cost-basis records before harvesting. Did you buy this security in the past 30 days? If so, wait to harvest (or harvest a different position).

  2. Use the full 60-day window in your planning. When tracking wash-sale risk, think: "30 days in the past + 30 days in the future."

  3. Document harvests and purchases chronologically. A timeline spreadsheet prevents this error.

Mistake 5: Cascading wash-sale adjustments across years​

Wash-sale adjustments don't disappear; they carry forward to the next purchase. If you repeatedly trigger wash-sales on the same security, the adjustments compound, creating a tax mess that's hard to untangle.

Scenario: The cascading disaster​

Year 1, January:

  • Buy AAPL: 100 shares at $150 = $15,000 cost basis.

Year 2, December:

  • Sell AAPL at $130 (realized loss: $2,000).
  • Then buy AAPL again Jan 5 of the next year at $135 (100 shares = $13,500).
  • Wash-sale: The $2,000 loss from Year 2 is disallowed and added to the Year 3 purchase cost basis: $13,500 + $2,000 = $15,500 (adjusted basis).

Year 3, June:

  • Sell AAPL at $140 (100 shares = $14,000).
  • Calculated loss: $14,000 - $15,500 = -$1,500 loss.
  • But you think your cost basis is $15,000 (the original purchase), not $15,500, so you report a $1,000 loss.

Year 4, April (tax filing):

  • IRS 1099-B shows proceeds of $14,000.
  • Your Form 8949 shows cost basis of $15,000 and loss of $1,000.
  • But the IRS's tracking shows cost basis should be $15,500 and loss should be $1,500.
  • CP2000 notice arrives: "You underreported loss by $500."

The error cascades across multiple years if you don't track wash-sale adjustments meticulously.

Prevention​

  1. Maintain a wash-sale adjustment log. Dedicate a column in your spreadsheet to track all adjustments. After each sale, update future cost-basis entries.

  2. Review cost-basis before every sale. Don't assume your original cost is correct; check your spreadsheet for any wash-sale adjustments that apply.

  3. Use brokerage cost-basis tracking tools. Most major brokerages (Fidelity, Schwab, Vanguard, E*TRADE) have tools that calculate cost basis including wash-sale adjustments. Use them as a secondary check.

Mistake 6: Harvesting in December, forgetting about January purchases​

A variation of the wash-sale window mistake: investors harvest losses in December (for the current year's tax benefit) but then make unrelated January purchases of the same security.

Scenario: The holiday harvest mistake​

December 28, Year 1:

  • You harvest a $50,000 loss from Nvidia in your taxable account (sell at loss).
  • You plan to use the tax benefit on your Year 1 return (filed April 2025).

January 8, Year 2:

  • You receive a year-end bonus and decide to invest in growth stocks.
  • You buy $50,000 of Nvidia shares in your taxable account (still bullish on the company).

Tax consequence:

  • Wash-sale violation: You bought Nvidia 11 days after selling, clearly within the 30-day window.
  • Disallowed loss: $50,000.
  • Tax owed: $12,000–$18,500 (depending on bracket) plus penalties.

Prevention​

  1. Set a 30-day reminder after harvesting. Use your phone calendar: "Nvidia harvest on Dec 28—can't buy until Jan 28."

  2. Track harvests across year-boundaries. Many investors think of taxes in terms of calendar years, forgetting that the 30-day window doesn't respect December 31.

  3. Consider harvesting after January 1 (not late December). This way, the 30-day restriction falls within the same calendar year, reducing confusion.

Mistake 7: Forgetting about inherited shares and stepped-up basis​

Less common but costly: if you inherit shares, they receive a stepped-up basis (fair market value at the date of death). If you then harvest losses, you must use the stepped-up basis, not the decedent's original cost.

Scenario: The inherited shares loss harvest​

Parent dies on January 1, 2024:

  • Parent owned Apple, original cost basis $50,000, now worth $200,000.
  • Child inherits 100 shares with a stepped-up basis of $200,000 (FMV at death).

August 2024 (8 months after inheritance):

  • Child sells Apple at $180,000 (market has declined).
  • Child calculates loss: $180,000 - original parental cost $50,000 = $130,000 gain (incorrect).
  • Actually, the correct loss: $180,000 - stepped-up basis $200,000 = $20,000 loss.

Tax consequence:

  • If child doesn't use the stepped-up basis, they'll overreport the loss by $110,000.
  • Or if they underreport the gain, IRS will flag it on a CP2000 notice.

Prevention​

  1. Document stepped-up basis for all inherited securities. Keep a copy of the death certificate, estate appraisal, and fair market value (FMV) statement.

  2. Use FMV as cost basis for inherited shares. Never use the decedent's original cost basis.

  3. Consult a CPA when inheriting significant securities. The basis step-up is valuable but requires careful documentation.

Mistake checklist before harvesting​

Common mistakes by frequency​

MistakeFrequencyTypical CostPrevention
Spousal account wash-saleVery common$5,000–$15,000Spouse coordination
DRIP reinvestmentCommon$3,000–$10,000Disable DRIP
IRA purchase wash-saleModerately common$2,000–$8,00030-day calendar
Look-back missedLess common$1,000–$5,000Review cost basis
Cascading adjustmentsRare$500–$3,000Track adjustments

Next​

We've explored the most common TLH mistakes. Next, we'll examine a related but distinct strategy: tax-gain harvesting, which is most useful in low-income years or before retirement, and how it differs from tax-loss harvesting.